#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <deque>
#include <cmath>
#include <climits>
#include <cstring>
#include <iomanip>
#include <numeric>
#include <functional>
#include <bitset>
#include <unordered_map>
#include <unordered_set>
#include <chrono>
#include <random>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define rep(a,b) for(int a = 0;a<b;a++)
#define st first
#define nd second
#define pb push_back
#define all(a) a.begin(),a.end()
const int inf = 1e9;
const ll infl = 1e18;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, t;
cin >> n >> t;
vector<int> a(n);
rep(i, n){
cin>>a[i];
}
rep(i, n){
a[i]%=t;
}
sort(all(a));
int w = abs(a[0] - a[n-1]);
rep(i, n-1){
a[i]+=t;
w = min(w, abs(a[i+1] - a[i]));
}
cout << (w+1)/2 << "\n";
return 0;
}
