#include <bits/stdc++.h>
using namespace std;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

int main() {
    int n, x; cin >> n >> x;
    auto s = vec<int>(uns, n);
    for (auto &e : s) cin >> e;

    int64_t sum = 0;
    for (auto e : s) {
        sum += x - e;
    }

    for (auto e : s) {
        if (e % 2 == 0 && sum - (x - e) + (x - e / 2) == x) {
            cout << e / 2 << endl;
            return 0;
        }
    }
}