// File roomtemp.cpp created on 28.09.2025 at 18:55:10
#include <bits/stdc++.h>
using i64 = long long;
#ifdef DEBUG
#include "/home/ahmetalp/Desktop/Workplace/debug.h"
#else
#define debug(...) void(23)
#endif
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int N, T;
std::cin >> N >> T;
std::vector<int> A(N);
for (int i = 0; i < N; ++i) {
std::cin >> A[i];
A[i] %= T;
}
std::sort(A.begin(), A.end());
debug(A);
if (A[0] == A[N - 1]) {
std::cout << "0\n";
return 0;
}
int ans = T - A[N - 1] + A[0];
for (int i = 0; i + 1 < N; ++i) {
if (A[i] == A[i + 1]) {
continue;
}
ans = std::max(ans, A[i + 1] - A[i]);
}
debug(ans);
std::cout << (T - ans + 1) / 2 << '\n';
return 0;
}
