#include<iostream>
using namespace std;
int main(){ 
	int n,k,l,w,b[100005];
	cin>>n>>k;
	for(int i = 0;i < n;i++){
		cin>>l>>w;
		int mn = min(l,w);
		for(int j = 1;j <= mn;j++){
			b[j] += (l/j)*(w/j); 
		}
	}
	int left = 1,right = t,mid = 0;
	while(1){
		mid = (left + right)/2;
		if(b[mid] < k) right = mid;
		else left = mid;
		if(b[mid] >= k&&b[mid+1] <k){
			cout<<mid;
			break;
		}
	}
	return 0;
}