#include <bits/stdc++.h>
using namespace std;
using ll=long long;

int main(){
	int n;
	cin>>n;
	vector<ll> a(3);
	for(int i=0;i<n;i++){
		ll s,t;
		cin>>s>>t;
		if(s%8==0)a[2]+=t;
		else if(s%4==0)a[1]+=t;
		else if(s%2==0)a[0]+=t;
	}
	ll ans=a[2];
	if(a[1]>=a[0]){
		ans+=a[0];
		a[1]-=a[0];
		ans+=a[1]/2;
	}else{
		ans+=a[1];
		a[0]-=a[1];
		ans+=a[0]/3;
	}
	cout<<ans<<endl;
}