description: You are given n segments on a number line, numbered from 1 to n. The i-th segments covers all integer points from l_i to r_i and has a value w_i.
  
  You are asked to select a subset of these segments (possibly, all of them). Once the subset is selected, it's possible to travel between two integer points if there exists a selected segment that covers both of them. A subset is good if it's possible to reach point m starting from point 1 in arbitrary number of moves.
  
  The cost of the subset is the difference between the maximum and the minimum values of segments in it. Find the minimum cost of a good subset.
  
  In every test there exists at least one good subset.
  
  Input
  
  The first line contains two integers n and m (1 ≤ n ≤ 3 ⋅ 10^5; 2 ≤ m ≤ 10^6) — the number of segments and the number of integer points.
  
  Each of the next n lines contains three integers l_i, r_i and w_i (1 ≤ l_i < r_i ≤ m; 1 ≤ w_i ≤ 10^6) — the description of the i-th segment.
  
  In every test there exists at least one good subset.
  
  Output
  
  Print a single integer — the minimum cost of a good subset.
  
  Examples
  
  Input
  
  
  5 12
  1 5 5
  3 4 10
  4 10 6
  11 12 5
  10 12 3
  
  
  Output
  
  
  3
  
  
  Input
  
  
  1 10
  1 10 23
  
  
  Output
  
  
  0
solution: # ------------------- fast io --------------------
  import os
  import sys
  from io import BytesIO, IOBase
  
  BUFSIZE = 8192
  
  
  class FastIO(IOBase):
      newlines = 0
      
      def __init__(self, file):
          self._fd = file.fileno()
          self.buffer = BytesIO()
          self.writable = "x" in file.mode or "r" not in file.mode
          self.write = self.buffer.write if self.writable else None
      
      def read(self):
          while True:
              b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
              if not b:
                  break
              ptr = self.buffer.tell()
              self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
          self.newlines = 0
          return self.buffer.read()
      
      def readline(self):
          while self.newlines == 0:
              b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
              self.newlines = b.count(b"\n") + (not b)
              ptr = self.buffer.tell()
              self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
          self.newlines -= 1
          return self.buffer.readline()
      
      def flush(self):
          if self.writable:
              os.write(self._fd, self.buffer.getvalue())
              self.buffer.truncate(0), self.buffer.seek(0)
  
  
  class IOWrapper(IOBase):
      def __init__(self, file):
          self.buffer = FastIO(file)
          self.flush = self.buffer.flush
          self.writable = self.buffer.writable
          self.write = lambda s: self.buffer.write(s.encode("ascii"))
          self.read = lambda: self.buffer.read().decode("ascii")
          self.readline = lambda: self.buffer.readline().decode("ascii")
  
  
  sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
  input = lambda: sys.stdin.readline().rstrip("\r\n")
  
  # ------------------- fast io --------------------
  from math import ceil
  
  
  def prod(a, mod=10 ** 9 + 7):
      ans = 1
      for each in a:
          ans = (ans * each) % mod
      return ans
  
  
  def gcd(x, y):
      while y:
          x, y = y, x % y
      return x
  
  
  def lcm(a, b): return a * b // gcd(a, b)
  
  
  def binary(x, length=16):
      y = bin(x)[2:]
      return y if len(y) >= length else "0" * (length - len(y)) + y
  
  
  from math import inf, log2
  
  
  class LazySegmentTree:
      def __init__(self, array, func=max):
          self.n = len(array)
          self.size = 2 ** (int(log2(self.n - 1)) + 1) if self.n != 1 else 1
          self.func = func
          self.default = 0 if self.func != min else inf
          self.data = [self.default] * (2 * self.size)
          self.lazy = [0] * (2 * self.size)
          self.process(array)
      
      def process(self, array):
          self.data[self.size: self.size + self.n] = array
          for i in range(self.size - 1, -1, -1):
              self.data[i] = self.func(self.data[2 * i], self.data[2 * i + 1])
      
      def push(self, index):
          """Push the information of the root to it's children!"""
          self.lazy[2 * index] += self.lazy[index]
          self.lazy[2 * index + 1] += self.lazy[index]
          self.data[2 * index] += self.lazy[index]
          self.data[2 * index + 1] += self.lazy[index]
          self.lazy[index] = 0
      
      def build(self, index):
          """Build data with the new changes!"""
          index >>= 1
          while index:
              self.data[index] = self.func(self.data[2 * index], self.data[2 * index + 1]) + self.lazy[index]
              index >>= 1
      
      def query(self, alpha, omega):
          """Returns the result of function over the range (inclusive)!"""
          res = self.default
          alpha += self.size
          omega += self.size + 1
          for i in range(len(bin(alpha)[2:]) - 1, 0, -1):
              self.push(alpha >> i)
          for i in range(len(bin(omega - 1)[2:]) - 1, 0, -1):
              self.push((omega - 1) >> i)
          while alpha < omega:
              if alpha & 1:
                  res = self.func(res, self.data[alpha])
                  alpha += 1
              if omega & 1:
                  omega -= 1
                  res = self.func(res, self.data[omega])
              alpha >>= 1
              omega >>= 1
          return res
      
      def update(self, alpha, omega, value):
          """Increases all elements in the range (inclusive) by given value!"""
          alpha += self.size
          omega += self.size + 1
          l, r = alpha, omega
          while alpha < omega:
              if alpha & 1:
                  self.data[alpha] += value
                  self.lazy[alpha] += value
                  alpha += 1
              if omega & 1:
                  omega -= 1
                  self.data[omega] += value
                  self.lazy[omega] += value
              alpha >>= 1
              omega >>= 1
          self.build(l)
          self.build(r - 1)
  
  for _ in range(int(input()) if not True else 1):
      #n = int(input())
      n, m = map(int, input().split())
      # a, b = map(int, input().split())
      # c, d = map(int, input().split())
      # a = list(map(int, input().split()))
      # b = list(map(int, input().split()))
      # s = input()
      edges = []
      for i in range(n):
          l, r, w = map(int, input().split())
          edges += [(l, r, w)]
      edges = sorted(edges, key=lambda x: x[2])
      st = LazySegmentTree([0.0]*(2*m+1), func=min)
      i = j = 0
      ans = 10**18
      st.update(2 * edges[0][0], 2 * edges[0][1], 1)
      while i < len(edges) and j < len(edges):
          if st.query(2, 2*m):
              ans = min(ans, edges[j][2] - edges[i][2])
              st.update(2 * edges[i][0], 2 * edges[i][1], -1)
              i += 1
          else:
              j += 1
              if j < len(edges):
                  st.update(2 * edges[j][0], 2 * edges[j][1], 1)
      print(ans)