#include <bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define fi first
#define se second
const int N = 5e5+5;
int n,t,a[N];
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> t;
for(int i = 1; i <= n; i++) cin >> a[i];
sort(a+1,a+n+1);
for(int i = 2; i <= n; i++){
int x = (a[i]-a[1])/t;
a[i] -= x*t;
}
sort(a+1,a+n+1);
int ans = (a[n]-a[1]+1)/2;
for(int i = 2; i <= n; i++){
int x = a[n]-t;
int y = a[i]-t;
int z = a[i-1];
ans = min(ans,(max({x,y,z})-min({x,y,z})+1)/2);
}
cout << ans;
}
