#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<ll,ll> P;
typedef modint1000000007 mint;
#define rep(i,a,b) for(ll i=a;i<b;i++)
#define rrep(i,a,b) for(ll i=a;i>=b;i--)
ll n,x;
ll a[200005],b[200005],s;
int main(void){
    cin.tie(0);
    ios::sync_with_stdio(0);
    cin>>n>>x;
    rep(i,0,n){
        cin>>a[i];
        b[i]=x-a[i];
        s+=b[i];
    }
    rep(i,0,n){
        if(a[i]%2==0){
            if(s-b[i]+x-a[i]/2==x){
                cout<<a[i]/2<<endl;
                return 0;
            }
        }
    }

}