#include<bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int,int>
#define fi first
#define se second
const int N = 3e5+5;
int n,m,a[N],b[N];
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m;
for(int i = 1; i <= n; i++) cin >> a[i];
for(int i = 1; i <= n; i++) cin >> b[i];
int l = 1;
int r = 1e18;
int ans = 0;
while(l <= r){
int mid = (l+r)/2;
int rem = n*m;
for(int i = 1; i <= n; i++){
if(a[i] > b[i]){
int aqua = (mid+a[i]-1)/a[i];
aqua = min(aqua,m);
int emilia = mid-a[i]*aqua;
rem -= aqua;
if(emilia > 0){
int subaru = (emilia+b[i]-1)/b[i];
rem -= subaru;
}
}
else{
int ram = (mid+b[i]-1)/b[i];
rem -= ram;
}
if(rem < 0) break;
}
if(rem >= 0){
ans = mid;
l = mid+1;
}
else r = mid-1;
}
cout << ans;
}
