#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
signed main(){
    int n, t; cin >> n >> t;
    vector<int> a(n);
    for (auto &i : a) cin >> i;
    for (auto &i : a) i %= t;
    sort(a.begin(), a.end());
    int ans = 1e18;
    for (int i = 0; i < n; i++){
    	ans = min(ans, a.back() - a[i]);
    	a.push_back(a[i] + t);
    }
	cout << (ans + 1) / 2 << endl;
	
	return 0;
}
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