#include <bits/stdc++.h>
using namespace std;
//#define USACO
#define fi first
#define se second
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
#define ALL(v) (v).begin(), (v).end()
#define BIT(i) (1LL << (i))
#define MASK(x, i) (((x) >> (i)) & 1)
#define REP(i, v) for( __typeof((v).begin()) i = (v).begin(); i != (v).end(); ++ i)
#define FOR(i, a, b) for(int i = (a), _b = (b); i <= _b; ++ i)
#define FORD(i, b, a) for(int i = (b), _a = (a); i >= _a; -- i)
const string NAME = "BAITAP";
const string name = "";
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
const int mod = 998244353;
const int mxN = 5e5 + 5;
int N, T;
vector<int> A(mxN);
void init(void){
cin >> N >> T;
FOR(i, 1, N){
cin >> A[i];
A[i] %= T;
}
}
void process(void){
sort(A.begin() + 1, A.begin() + 1 + N);
int ans = A[N] - A[1];
FOR(i, 1, N){
ans = min(ans, T - (A[i + 1] - A[i]));
}
cout << ((ans + 1) >> 1);
}
signed main(void){
ios::sync_with_stdio(false);
cin.tie(nullptr);
#ifdef LOCAL
freopen((NAME + ".INP").c_str(), "r", stdin);
freopen((NAME + ".OUT").c_str(), "w", stdout);
#elif defined(USACO)
freopen((name + ".in").c_str(), "r", stdin);
freopen((name + ".out").c_str(), "w", stdout);
#endif
init();
process();
cerr << "\nTime elapsed: " << TIME << "s.\n";
}
