#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <vector>
#include <unordered_set>
#include <map>
#include <utility>
#include <list>
#include <math.h>
#include <algorithm>
#include <numeric>
#include <bitset>

typedef long long ll;
const int INF=10000;
using namespace std;
/*
int binary(int a){
    for (int i=0;a>0;i++)
    {
        ans=ans+(a%2)*pow(10,i);
        a=a/2;
    }
    return ans;
}*/
ll dx[4]={0,1,0,1};
ll dy[4]={0,0,1,1};

int main(){
    ll n;
    ll x;
    cin>>n>>x;
    vector<ll> S(n);
    vector<ll> ans(n);
    ll aaa=0;
    for(int i=0;i<n;i++)
    {
        cin>>S[i];
        ans[i]=x-S[i];
        aaa+=S[i];
//        aaa[i]=(x-ans[i])/2;
    }
    for(int i=0;i<n;i++)
    {
        if(aaa-S[i]/2==x*(n-1))
        {
            cout<<S[i]/2<<endl;
            return 0;
        }
    }
 //   return 0;

}