description: The numbers 1,   2,   ...,   n ⋅ k are colored with n colors. These colors are indexed by 1,   2,   ...,   n. For each 1 ≤ i ≤ n, there are exactly k numbers colored with color i.
  
  Let [a,   b] denote the interval of integers between a and b inclusive, that is, the set \\{a,   a + 1,   ...,   b\}. You must choose n intervals [a_1,   b_1],   [a_2,   b_2],   ..., [a_n,   b_n] such that: 
  
    * for each 1 ≤ i ≤ n, it holds 1 ≤ a_i < b_i ≤ n ⋅ k; 
    * for each 1 ≤ i ≤ n, the numbers a_i and b_i are colored with color i; 
    * each number 1 ≤ x ≤ n ⋅ k belongs to at most \left⌈ (n)/(k - 1) \right⌉ intervals. 
  
  
  
  One can show that such a family of intervals always exists under the given constraints.
  
  Input
  
  The first line contains two integers n and k (1 ≤ n ≤ 100, 2 ≤ k ≤ 100) — the number of colors and the number of occurrences of each color.
  
  The second line contains n ⋅ k integers c_1,   c_2,   ...,   c_{nk} (1 ≤ c_j ≤ n), where c_j is the color of number j. It is guaranteed that, for each 1 ≤ i ≤ n, it holds c_j = i for exactly k distinct indices j.
  
  Output
  
  Output n lines. The i-th line should contain the two integers a_i and b_i.
  
  If there are multiple valid choices of the intervals, output any.
  
  Examples
  
  Input
  
  
  4 3
  2 4 3 1 1 4 2 3 2 1 3 4
  
  
  Output
  
  
  4 5
  1 7
  8 11
  6 12
  
  Input
  
  
  1 2
  1 1
  
  
  Output
  
  
  1 2
  
  
  Input
  
  
  3 3
  3 1 2 3 2 1 2 1 3
  
  
  Output
  
  
  6 8
  3 7
  1 4
  
  Input
  
  
  2 3
  2 1 1 1 2 2
  
  
  Output
  
  
  2 3
  5 6
  
  Note
  
  In the first sample, each number can be contained in at most \left⌈ (4)/(3 - 1) \right⌉ = 2 intervals. The output is described by the following picture:
  
  <image>
  
  In the second sample, the only interval to be chosen is forced to be [1,   2], and each number is indeed contained in at most \left⌈ (1)/(2 - 1) \right⌉ = 1 interval.
  
  In the third sample, each number can be contained in at most \left⌈ (3)/(3 - 1) \right⌉ = 2 intervals. The output is described by the following picture:
  
  <image>
solution: 
  def naiveSolve():
      
      
      
      return
  
  
  
  def main():
      
      n,k=readIntArr()
      c=readIntArr()
      
      a=[-1]*(n+1)
      b=[-1]*(n+1)
      
      prev=[-1]*(n+1) # previous index of each color
      cnts=[0]*(n*k) # counts of intervals including each c index
      limit=(n+k-2)//(k-1)
      
      start=0 # start idx of current "n/(k-1) batch"
      for i in range(n*k):
          if prev[c[i]]>=start and a[c[i]]==-1:
              a[c[i]]=prev[c[i]]
              b[c[i]]=i
              for j in range(prev[c[i]],i+1):
                  cnts[j]+=1
                  if cnts[j]==limit: # update start
                      start=i+1
                      # print('i:{} start:{}'.format(i,start))
          else:
              prev[c[i]]=i
      
      for i in range(1,n+1):
          print('{} {}'.format(a[i]+1,b[i]+1))
      
      return
  
  # n=4,k=3,limit=2
  # 2 4 3 1 1 4 2 3 2 1 3 4
  #       < >
  #   <       >
  #             <   >
  #               <     >
  
  # n=3,k=3,limit=2
  # 3 1 2 3 2 1 2 1 3
  # <     >
  #     <   >
  #           <   >
  
  import sys
  input=sys.stdin.buffer.readline #FOR READING PURE INTEGER INPUTS (space separation ok)
  # input=lambda: sys.stdin.readline().rstrip("\r\n") #FOR READING STRING/TEXT INPUTS.
  
  def oneLineArrayPrint(arr):
      print(' '.join([str(x) for x in arr]))
  def multiLineArrayPrint(arr):
      print('\n'.join([str(x) for x in arr]))
  def multiLineArrayOfArraysPrint(arr):
      print('\n'.join([' '.join([str(x) for x in y]) for y in arr]))
   
  def readIntArr():
      return [int(x) for x in input().split()]
  # def readFloatArr():
  #     return [float(x) for x in input().split()]
   
  def makeArr(defaultValFactory,dimensionArr): # eg. makeArr(lambda:0,[n,m])
      dv=defaultValFactory;da=dimensionArr
      if len(da)==1:return [dv() for _ in range(da[0])]
      else:return [makeArr(dv,da[1:]) for _ in range(da[0])]
   
  def queryInteractive(l,r):
      print('? {} {}'.format(l,r))
      sys.stdout.flush()
      return int(input())
   
  def answerInteractive(x):
      print('! {}'.format(x))
      sys.stdout.flush()
   
  inf=float('inf')
  # MOD=10**9+7
  MOD=998244353
  
  from math import gcd,floor,ceil
  # from math import floor,ceil # for Python2
   
  for _abc in range(1):
      main()