num27

#include <iostream>
#include <fstream>
using namespace std;

int main() {
    int n, i, a, b, s = 0, d = 2000000000, c;
    cin >> n;
    for (i = 0; i < n; i++) {
        cin >> a >> b;
        s += min(a, b);
        c = abs(a - b);
        if (c % 3 != 0 && c < d)
            d = c;
    }
    if (s % 3 == 0)
        s -= d;
    cout << s;
    return 0;
}