#include<iostream>
using namespace std;
int n;
double ans,b;
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	cin>>n;
	for(int i=1;i<=n<<1;i++){
        cin>>b;
        ans+=b;
	}
	ans/=2;
	cout<<ans;
	return 0;
}