#include<bits/stdc++.h>
#define int long long
using namespace std;
vector<int> a;
signed main(){
int n,js=0;
while(1){
if(n==0){
break;
}
cin>>n;
a.push_back(n);
js++;
}
js-=1;
if(js%2==0){
cout<<a[js/2]+a[js/2-1];
}else{
cout<<a[js/2];
}
return 0;
}