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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    array<ll, 4> cnt{};
    for(int i = 0; i < n; i++){
        int a, b;
        cin >> a >> b;
        if(a % 8 == 0){
            cnt[3] += b;
            continue;
        }
        if(a % 4 == 0){
            cnt[2] += b;
            continue;
        }
        if(a % 2 == 0){
            cnt[1] += b;
            continue;
        }
    }
    ll ans = cnt[3];
    ll d = min(cnt[2], cnt[1]);
    ans += d;
    cnt[2] -= d, cnt[1] -= d;
    ans += cnt[2] / 2;
    ans += cnt[1] / 3;
    cout << ans << '\n';
}