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

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

  int n, x;
  cin >> n >> x;
  vector<int> s(n);
  long long sum = 0;
  for (int i = 0; i < n; i++) cin >> s[i], sum += s[i];

  long long k = (long long)(n - 1) * x;
  for (int i = 0; i < n; i++) {
    if (s[i] % 2 == 0 && sum - s[i] / 2 == k) {
      cout << s[i] / 2 << '\n';
      return 0;
    }
  }
}