#include <bits/stdc++.h>
using namespace std;
const int mxn = 5e5 + 10;
int n, m, a[mxn];
vector<int> vec;
int main() {
cin >> n >> m;
for(int i = 0; i < n; i++) {
cin >> a[i];
a[i] %= m;
vec.push_back(a[i]);
}
sort(vec.begin(), vec.end());
vec.erase(unique(vec.begin(), vec.end()), vec.end());
if(vec.size() == 1) {
cout << 0 << endl;
return 0;
}
vec.push_back(vec[0]);
int ans = INT_MAX;
for(int i = 1; i < vec.size(); i++) {
int t = vec[i] - vec[i - 1];
if(t < 0) t += m;
t = max(t, m - t);
ans = min(ans, (t + 1) / 2);
}
cout << ans << endl;
return 0;
}
