#include<bits/stdc++.h>
using namespace std;
signed main() {
int n, t; cin >> n >> t;
vector<int> a(n);
for(int i=0; i<n; i++) cin >> a[i];
for(int i=0; i<n; i++) a[i]%=t;
sort(a.begin(), a.end());
vector<int> cur={a[0]};
for(int i=1; i<n; i++) if(a[i] != a[i-1]) cur.push_back(a[i]);
a=cur;
vector<int> aa;
for(int i=0; i<a.size(); i++) aa.push_back(a[i]-t);
for(int i=0; i<a.size(); i++) aa.push_back(a[i]);
for(int i=0; i<a.size(); i++) aa.push_back(a[i]+t);
// for(auto x : aa) cout << x << ' ';
// cout << endl;
int best=t/2, half=t/2;
for(int i=0; i<a.size(); i++) {
auto prev = lower_bound(aa.begin(), aa.end(), a[i]-half), aft = upper_bound(aa.begin(), aa.end(), a[i]+half);
aft--;
best=min(best, max(a[i]-aa[prev-aa.begin()], aa[aft-aa.begin()]-a[i]));
}
//cout << best << endl;
a.push_back(a[0]+t);
// for(auto x : a) cout << x << ' ';
// cout << endl;
// cout << half << endl;
for(int i=1; i<a.size(); i++) {
int mid1 = (a[i]-a[i-1])/2 + a[i-1], mid2=(a[i]-a[i-1]+1)/2 + a[i-1];
//cout << mid1 << ' ' << mid2 << endl;
auto prev = lower_bound(aa.begin(), aa.end(), mid1-half), aft = upper_bound(aa.begin(), aa.end(), mid1+half);
aft--;
best=min(best, max(mid1-aa[prev-aa.begin()], aa[aft-aa.begin()]-mid1));
prev = lower_bound(aa.begin(), aa.end(), mid2-half); aft = upper_bound(aa.begin(), aa.end(), mid2+half);
aft--;
best=min(best, max(mid2-aa[prev-aa.begin()], aa[aft-aa.begin()]-mid2));
}
cout << best;
return 0;
}
