#include <bits/stdc++.h>
using namespace std;
#define _GLIBCXX_DEBUG
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define ll long long
int main(){
    int n, x;
    cin >> n >> x;
    vector<int> s(n);
    vector<int> a(n);
    rep(i, n){
        cin >> s[i];
        a[i] = x - s[i];
    }
    int s2 = 0;
    rep(i, n) s2 += a[i];
    rep(i, n) {
        if (x - s2 == s[i]/2){
            cout << s[i]/2 << endl;
            return 0;
        }
    }
}