#include "atcoder/fenwicktree.hpp"
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;

using isize = size_t;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128_t;
using u128 = __uint128_t;
using f64 = long double;
using p2 = pair<i64, i64>;
using el = tuple<i64, i64, i64>;
using mint = atcoder::modint998244353;

void _main();
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  _main();
}

i64 pow(i64 x, i64 n) {
  i64 res = 1;
  i64 t = x;
  while (n > 0) {
    if (n & 1) {
      res = res * t;
    }
    t = t * t;
    n >>= 1;
  }
  return res;
}
i64 pow(i64 x, i64 n, i64 m) {
  i64 res = 1;
  i64 t = x % m;
  while (n > 0) {
    if (n & 1) {
      res = res * t % m;
    }
    t = t * t % m;
    n >>= 1;
  }
  return res;
}

void _main() {
  i64 n;
  cin >> n;
  vector<i64> cnt(4, 0);
  for (i64 i = 0; i < n; i++) {
    i64 a, b;
    cin >> a >> b;
    i64 c = 0;
    while (a % 2 == 0) c++, a /= 2;
    c = min(c, 3ll);
    cnt[c] += b;
  }
  i64 ans = 0;
  ans += cnt[3];
  i64 d = min(cnt[1], cnt[2]);
  ans += d;
  cnt[1] -= d, cnt[2] -= d;
  ans += cnt[1] / 3;
  ans += cnt[2] / 2;
  cout << ans << "\n";
}