#include <bits/stdc++.h>

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
const int N = 2000086, MOD = 998244353, INF = 0x3f3f3f3f;
ll res;
int n, m, cnt, w[N];


ll s[4];
int main() {
    cin >> n;
    for (int i = 1, a, b; i < n + 1; i++) {
        scanf("%d%d", &a, &b);
        int c = 0;
        while (c != 3 && a % 2 == 0) a /= 2, c++;
        s[c] += b;
    }
    res = s[3];
    ll t = min(s[2], s[1]);
    res += min(s[2], s[1]);
    s[2] -= t, s[1] -= t;
    res += (s[2] >> 1) + (s[1] / 3);
    printf("%lld\n", res);
    return 0;
}