#include<bits/stdc++.h> using namespace std; #define int long long #define REP(i,m,n) for(int i=(m);i<(n);i++) #define rep(i,n) REP(i,0,n) #define pb push_back #define all(a) a.begin(),a.end() #define rall(c) (c).rbegin(),(c).rend() #define mp make_pair #define endl '\n' #define vec vector<ll> #define mat vector<vector<ll> > #define fi first #define se second #define double long double typedef long long ll; typedef unsigned long long ull; typedef pair<ll,ll> pll; //typedef long double ld; typedef complex<double> Complex; const ll INF=1e9+7; const ll inf=INF*INF; const ll mod=998244353; const ll MAX=140010; signed main(){ ll n;cin>>n; ll x;cin>>x; vector<ll>s(n); ll sum=0; rep(i,n){ cin>>s[i]; sum+=s[i]; } rep(i,n){ if(s[i]%2!=0)continue; if(sum-s[i]/2==x*(n-1)){ cout<<s[i]/2<<endl; return 0; } } }