// 23 - 12 - 23
#include<bits/stdc++.h>
using namespace std;
#define read() ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define day() time_t now = time(0);char* x = ctime(&now);cerr<<"Right Now Is : "<<x<<"\n"
#define int long long
#define ii pair<int,int>
#define X first
#define Y second
const long long MAX = (int)5e5 + 5;
const long long INF = (int)1e9;
const long long MOD = (int)1e9 + 7;
int n,t;
int a[MAX * 2];
signed main(){
cin >> n >> t;
for(int i = 1;i <= n;i++)cin >> a[i];
for(int i = 1;i <= n;i++){
a[i] %= t;
}
sort(a + 1,a + 1 + n);
//for(int i = 1;i <= n;i++)cout << a[i] << " \n";
int res = INF;
for(int i = 1;i <= n;i++){
res = min(res,(a[i + n - 1] - a[i] + 1) / 2);
a[i + n] = a[i] + t;
}
cout << res;
}
