/* Author : Mychecksdead */
#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define MOD (1000000000+7)
#define MOD1 (998244353)
#define pb push_back
#define all(x) x.begin(), x.end()
#define en cout << '\n'
#define ff first
#define ss second
#define pii pair<int,int>
#define vi vector<int>
const int N = 1e6+100, M = 1e5+10, K = 52, MX = 30;
int n;
ll t, a[N];
ll get(ll x,ll y){
if(x>y) swap(x,y);
return min((y-x+1)/2, (x+t-y+1)/2);
}
void solve(){
cin >> n >> t;
for(int i = 1; i <= n; ++i){
cin >> a[i];
a[i] %= t;
}
sort(a+1, a+1+n);
ll ans = (a[n]-a[1]+1)/2;
for(int i = 1; i < n; ++i){
ans = min(ans, (a[i] + t - a[i + 1] + 1)/2);
}
cout << ans;
}
int main(){
cin.tie(0); ios::sync_with_stdio(0);
int tt = 1, aa;
// freopen("in.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
while(tt--){
solve();
en;
}
cerr<<"time taken : "<<(float)clock()/CLOCKS_PER_SEC<<" seconds\n";
return 0;
}
