#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("fast-math")
#pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx,tune=native")
mt19937 rng(time(NULL));
const int inf = 1e9 + 100;
const long long linf = 2e18;
const long long maxn = 3e5 + 100;
const int mod = 1e9 + 7;
int n, m;
bool f(vector<int> a, int x) {
  if (x >= (m - a[0])) a[0] = 0;
  for (int i = 1; i < n; ++i) {
    if (a[i] <= a[i - 1])
      a[i] += min(x, a[i - 1] - a[i]);
    else if (x >= (m - a[i] + a[i - 1]))
      a[i] = a[i - 1];
  }
  for (int i = 1; i < n; ++i)
    if (a[i - 1] > a[i]) return 0;
  return 1;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> m;
  vector<int> a(n);
  for (int i = 0; i < n; ++i) cin >> a[i];
  int l = 0, r = 1e6;
  while (l + 1 < r) {
    int c = (l + r) / 2;
    if (f(a, c))
      r = c;
    else
      l = c;
  }
  if (!f(a, l)) l++;
  cout << l;
  return 0;
}
