#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, x;
    cin >> n >> x;

    vector<int> s(n);
    ll t = 0;
    for (int i = 0; i < n; i++) {
        cin >> s[i];
        t += s[i];
    }

    for (int i = 0; i < n; i++) {
        if (s[i] % 2 == 0) {
            ll u = t - s[i] / 2;
            if (u % (n - 1) == 0) {
                u /= n - 1;
                if (u == x) {
                    cout << s[i] / 2 << endl;
                    exit(0);
                }
            }
        }
    }

    return 0;
}