#define _USE_MATH_DEFINES

#include <iostream>	//cin, cout
#include <vector>	//vector
#include <algorithm> //sort,min,max,count
#include <string>	//string,getline, to_string
#include <ios>		//fixed
#include <iomanip>	//setprecision
#include <utility> //swap, pair
#include <cstdlib>	//abs(int)
#include <cmath>	//sqrt,ceil,M_PI, pow, sin
#include <sstream>	//stringstream, getline
#include <numeric>	//gcd, accumlate
#include <deque>	//deque
#include <random>	//randam_device
#include <limits>	//numeric_limits

using namespace std;
constexpr long long int D_MOD = 1000000007;

int main() {

	long long int N, X;
	cin >> N >> X;

	long long int sum = 0;

	vector<int> S(N);
	for (int i = 0; i < N; i++) {
		cin >> S[i];
		sum += S[i];
	}

	long long int T = X * (N - 1);

	for (int i = 0; i < N; i++) {
		if (S[i] % 2 != 0) {
			continue;
		}
		else {
			if (sum - S[i] / 2 == T) {
				cout << S[i] / 2 << endl;
				return 0;
			}
		}
	}

	return 0;

}