#line 1 "main.cpp"
#include <iostream>
#include <numeric>
#include <vector>

using namespace std;
using lint = long long;
constexpr lint INF = 1LL << 60;

void solve() {
    int n;
    lint sum;
    cin >> n >> sum;

    vector<lint> xs(n), ys(n);
    for (int i = 0; i < n; ++i) {
        lint s;
        cin >> s;

        xs[i] = sum - s;
        if (s % 2 == 0) {
            ys[i] = sum - s / 2;
        } else {
            ys[i] = INF;
        }
    }

    lint nsum = accumulate(xs.begin(), xs.end(), 0LL);
    for (int i = 0; i < n; ++i) {
        if (nsum - xs[i] + ys[i] == sum) {
            cout << (sum - xs[i]) / 2 << "\n";
            return;
        }
    }
}

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

    solve();

    return 0;
}