#include <iostream>
#include <vector>
using namespace std;
using ll = long long;

int main() {
    ll N;
    cin >> N;
    vector<ll> A(N);
    vector<ll> B(N);
    for (ll i = 0; i < N; i++) {
        cin >> A[i] >> B[i];
    }

    vector<ll> divs(4, 0);
    for (ll i = 0; i < N; i++) {
        ll div_times = 0;
        for (ll j = 0; j < 3; j++) {
            if (A[i] % 2 != 0) {
                break;
            }
            A[i] /= 2;
            div_times++;
        }
        divs[div_times] += B[i];
    }
    ll p = min(divs[1], divs[2]);
    divs[1] -= p;
    divs[2] -= p;
    ll ans = p + divs[3];
    ans += divs[1] / 3;
    ans += divs[2] / 2;
    cout << ans << endl;
}