#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    int N;
    std::cin >> N;
    std::vector<int64_t> count(3);
    while (N--) {
        int A, B;
        std::cin >> A >> B;
        if (A % 2 > 0) continue;
        else if (A % 4 > 0) count[0] += B;
        else if (A % 8 > 0) count[1] += B;
        else count[2] += B;
    }
    int64_t result = std::min(count[0], count[1]);
    count[0] -= result;
    count[1] -= result;
    if (count[0]) result += count[0] / 3;
    else result += count[1] / 2;
    std::cout << result + count[2] << std::endl;
}