#include <bits/stdc++.h>
using namespace std;
#define int long long 

void doWork(){
	int n , m;
	cin >> n >> m;
	vector<int> a(n) , b(n);
	for (int i = 0 ; i < n;  i++) cin >> a[i];
	for (int i = 0 ; i < n ; i++) cin >> b[i];
	
	int l = 0 , r = 1e18 , md;
	while(l<=r){
		md = (l+r)/2;
		int sum = 0 ;
		for (int i = 0 ; i < n ; i++){
			sum += (md + b[i]-1)/b[i];
            if (sum > n*m) break;
		}
		if (sum <= n*m) l = md+1;
		else r = md-1; 
	}
	cout << l-1; 
}

signed main(){
	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    doWork();
}