#include <bits/stdc++.h>

using namespace std;
const int N = 110;
int n, k;
int w[N], h[N];
/*
2 6
4 3
5 4

答案：
2
*/
int main() {
    cin >> n >> k;
    for (int i = 1; i <= n; i++) cin >> w[i] >> h[i];

    for (int i = 1;; i++) {
        int cnt = 0;
        for (int j = 1; j <= n; j++)
            cnt += (w[j] / i) * (h[j] / i);

        if (cnt == k) {
            cout << i << endl;
            return 0;
        }
        if (cnt < k) {
            cout << -1 << endl;
            return 0;
        }
    }
    return 0;
}