#include <bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define pb push_back
#define int long long
#define pint pair<int, int>
#define vint vector<pair<int, int>>
const int mod = 1e9 + 7;
const int shrek = 5e5 + 5;
const int say = INT_MAX / 2;
const int gex = INT_MIN / 2;
const long long oo = 1e18;
signed main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, t; cin >> n >> t;
int a[n];
for(int i = 0; i < n; i++) {
cin >> a[i];
a[i] = a[i] % t;
}
sort(a, a + n);
int ans = (a[n - 1] - a[0] + 1) / 2;
for(int i = 0; i < n - 1; i++) {
ans = min(ans, (a[i] + t - a[i + 1] + 1) / 2);
}
cout << ans << '\n';
return 0;
}
