#include <bits/stdc++.h>

using namespace std;
const int N = 110;
const int INF = 0x3f3f3f3f;
int n, k;
int w[N], h[N];
int tmax = -INF;
/*
2 6
4 3
5 4

答案：
2
*/
// 检查x是否满足某种性质
bool check(int x) {
    int cnt = 0;
    for (int j = 1; j <= n; j++)
        cnt += (w[j] / x) * (h[j] / x);
    //以2为例，cnt=6 k=6 正合适
    //以1为例 cnt=32 k=6 cnt>k
    //所以最终的限制条件为cnt<=k
    return cnt <= k;
}
int main() {
    cin >> n >> k;
    for (int i = 1; i <= n; i++) {
        cin >> w[i] >> h[i];
        tmax = max(min(w[i], h[i]), tmax);
    }
    //二分查询
    int l = 1, r = tmax;
    while (l < r) {
        int mid = l + r >> 1;
        if (check(mid))
            r = mid;
        else
            l = mid + 1;
    }
    //也可能找不到答案
    int cnt = 0;
    for (int i = 1; i <= n; i++)
        cnt += (w[i] / l) * (h[i] / l);
    if (cnt < k)
        cout << -1 << endl;
    else
        cout << l << endl;
    return 0;
}