#include <iostream>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <limits.h>
#include <algorithm>
#include <math.h>
using namespace std;
int main()
{
iostream::sync_with_stdio(0);
cin.tie(0);
int n, t;
cin >> n >> t;
vector<int> a(n);
for (int i = 0; i < n; i++)
{
cin >> a[i];
a[i] %= t;
}
sort(a.begin(), a.end());
int bestrange = a.back() - a[0];
for (int i = 1; i < n; i++)
{
if (a[i - 1] + t - a[i] < bestrange) bestrange = a[i - 1] + t - a[i];
}
cout << (bestrange + 1) / 2;
}
