#include <algorithm>
#include <iostream>
#include <queue>
#include <utility>

using namespace std;

int N;
int A[1500], AA[1500], B[1500];
int cnt[1500];

int main() {
	cin >> N;
	for (int i = 0; i < N; i++) {
		cin >> A[i] >> B[i];
	}
	int res = N;
	for (int i = 0; i < N; i++) {
		priority_queue<pair<int, int> > P;
		for (int j = 0; j < N; j++) {
			AA[j] = A[j];
			cnt[j] = 0;
			P.push(make_pair(-(AA[j] * N + cnt[j]), j));
		}
		for (int j = 0; j < N; j++) {
			int k = (i + j) % N;
			pair<int, int> p = P.top();
			P.pop();
			cnt[p.second]++;
			AA[p.second] += B[k] / 2;
			P.push(make_pair(-(AA[p.second] * N - cnt[p.second]), p.second));
		}
		res = min(res, *max_element(cnt, cnt + N));
	}
	cout << res << endl;
	return 0;
}