#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

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

    int N, X;
    cin >> N >> X;
    vector<ll> S(N);
    ll sum = 0;
    for(int i = 0; i < N; ++i){
        cin >> S[i];
        sum += S[i];
    }
    
    for(int i = 0; i < N; ++i){
        if(S[i] % 2 == 1)   continue;
        sum -= S[i];
        sum += S[i] / 2;
        if(sum % (N - 1) == 0 && sum / (N - 1) == X){
            cout << S[i] / 2 << endl;
            return 0;
        }
        sum -= S[i] / 2;
        sum += S[i];
    }

    return 0;
}