#ifdef __AVX2__
#pragma GCC target "avx2"
#endif
#pragma GCC optimize "O3"
#pragma GCC optimize "unroll-loops"
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define int long long
#define elif else if
#define all(l) begin(l),end(l)
#define rall(l) rbegin(l),rend(l)
#define append push_back
#define print(l) for(auto i:l) cout<<i<<' '; cout<<endl;
#define pprint(a,b) cout<<a<<' '<<b<<endl;
#define inp(l) for(auto &i:l) cin>>i;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define pai make_pair
#define endl "\n"
#define pii pair<int,int>
#define fi first
#define se second
#define vec vector
// const int mod=998244353;
// const int mod1=998244353;
const int mod=1e9+7;
const int N=5e5+5;
int iter=1,itera=1;
void solve(){
int n,t;
cin>>n>>t;
vec<int>a(n);
inp(a);
for(auto &i:a) i%=t;
sort(all(a));
int mi=a[0],ma=a[n-1];
int ans=(ma-mi+1)/2;
for(int i=n-1;i>=1;i--){
ma=a[i-1];
a[i]-=t;
mi=a[i];
ans=min(ans,(ma-mi+1)/2);
}
cout<<ans<<endl;
}
signed main(){
// freopen("","r",stdin);
// freopen("","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
// cin>>itera;
for(iter=1;iter<=itera;iter++) solve();
}
