#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int n; cin >> n;
	vector<int>a(n), b(n);
	long long ans = 0;
	long long c0 = 0, c1 = 0;
	rep(i, n) {
		cin >> a[i] >> b[i];
		if (a[i] % 8 == 0) {
			ans += b[i];
		}
		else if (a[i] % 4 == 0) {
			c0 += b[i];
		}
		else if (a[i] % 2 == 0) {
			c1 += b[i];
		}
	}
	long long x = min(c0, c1);
	ans += x;
	c0 -= x;
	c1 -= x;
	x = c0 / 2;
	ans += x;
	c0 -= x * 2;
	ans += (c0 + c1) / 3;
	cout << ans << endl;
	return 0;
}