#include<bits/stdc++.h>
#define IOS ios_base::sync_with_stdio(false);cin.tie();cout.tie();
#define all(x) x.begin(), x.end()
#define int long long
#define pq priority_queue
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define pp pop_back
#define F first
#define S second
using namespace std;
void solve () {
int n, t;
cin >> n >> t;
vector<int> a(n);
for (auto &i: a) {cin >> i; i %= t;}
sort(all(a));
int mn = a[n-1] - a[0];
for (int i = 0; i < n - 1; i++) {
mn = min(mn, a[i] + t - a[i+1]);
}
cout << (mn + 1) / 2;
}
signed main() {IOS solve(); return 0;}
