#include <bits/stdc++.h>
using namespace std;
#define pb push_back
const int INF = 1e9;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, k;
cin >> n >> k;
vector<int> inp, arr;
for(int i=0; i<n; i++){
int x; cin >> x;
inp.pb(x);
}
sort(inp. begin(), inp.end());
for(int i=1; i<n; i++){
int diff = inp[i]-inp[0];
diff = diff/k; inp[i]-=diff*k;
}
sort(inp. begin(), inp.end());
arr.pb(inp[0]-k);
for(int i=1; i<n; i++){
arr.pb(inp[i]-k);
}
for(auto x:inp) arr.pb(x);
int out = INF;
for(int i=0; i<n; i++){
int diff = arr[i+n-1]-arr[i];
out = min(out, diff/2 + diff%2);
}
cout << out << '\n';
return 0;
}
