#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 3e5 + 10;
int a[N], b[N];
int n, m;
bool check(int x){
__int128_t remain = n * m;
for(int i = 0; i < n; i++){
__int128_t y = x;
if(b[i] > a[i]) a[i] = b[i];
__int128_t r1 = min((y + a[i] - 1) / a[i], (__int128_t) m);
remain -= r1;
y -= r1 * a[i];
__int128_t r2 = (y + b[i] - 1) / b[i];
if(r2 >= INT64_MAX) return false;
remain -= max((__int128_t) 0LL, r2);
}
return remain >= 0;
}
int32_t main(){
cin >> n >> m;
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;
while(l != r){
if(check((l + r + 1) / 2)){
l = (l + r + 1) / 2;
}else{
r = (l + r + 1) / 2 - 1;
}
}
cout << l << endl;
}
