#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int n, x;
    cin >> n >> x;
    vector<int> v(n);
    for (auto &&i : v) scanf("%d", &i);
    auto S = accumulate(v.begin(),v.end(), 0LL);
    for (int i = 0; i < n; ++i) {
        if(v[i]%2) continue;
        auto T = S - v[i]/2;
        if(T%(n-1)) continue;
        if(T/(n-1) == x){
            cout << v[i]/2 << "\n";
            return 0;
        }

    }
    return 0;
}