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

int main(){
    ll n; cin >> n;
    vector<ll> cnt(4);
    for(ll i = 0;i<n;i++){
        ll a,b; cin >> a >> b;
        ll div = 0;
        while(a % 2 == 0 && div < 3){
            div++;
            a /= 2;
        }
        cnt[div] += b;
    }
    ll ans = cnt[3];
    ll tmp = min(cnt[1],cnt[2]);
    ans += tmp;
    cnt[1] -= tmp;
    cnt[2] -= tmp;
    ans += cnt[1]/3;
    ans += cnt[2]/2;
    cout << ans << endl;
}