#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll n,a[100100],b[100100];
int main(){
	cin>>n;
	ll ans=0;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		ans+=a[i];
	}
	for(int i=1;i<=n;i++){
		cin>>b[i];
		ans+=b[i];
	}
	if(ans%2==0)  cout<<ans/2;
	else  cout<<(ans+1)/2;
	return 0;
}