#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--)
#define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++)
#define rrep2(ri,x,n) for(int ri = (int)(n-1); ri >= (int)(x); ri--)
#define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++)
#define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++)
#define ALL(x) x.begin(), x.end()
using ll = long long;
using namespace std;

int main(){
  int n, x;
  cin >> n >> x;
  vector<int> s(n);
  rep(i, n) cin >> s.at(i);
  ll sum = accumulate(ALL(s), 0LL);
  ll tot = (ll)x * (n-1);
  int ans = 0;
  rep(i, n){
    ll now = sum - s.at(i);
    now += s.at(i)/2;
    if(now == tot){
      ans = s.at(i)/2;
      break;
    }
  }
  cout << ans << endl;
  return 0;
}