#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll,ll> P;
#define REP(i,n) for(ll i=0;i<ll(n);i++)














int main(void){
	cin.tie(nullptr);  ios_base::sync_with_stdio(false);
	ll i,j;




	ll N;
	cin >> N;


	vector<ll> t(2,0);
	ll ans=0;
	for(i=1;i<=N;i++){

		ll A,B;
		cin >> A >> B;

		if(A%8==0) ans+=B;
		else{
			if(A%4==0) t[1]+=B;
			else if(A%2==0) t[0]+=B;
		}

	}


		if(t[0]>=t[1]) ans+=t[1]+(t[0]-t[1])/3;
		else ans+=t[0]+(t[1]-t[0])/2;



		cout << ans << endl;




	return 0;

}