#include<bits/stdc++.h>
#define int long long
#define ms(v) memset(v, -1, sizeof v)
#define pi pair<int, int>
#define pb push_back
#define fr first
#define sc second
#define srt(v) sort(v.begin(), v.end())
#define INF 1e15
#define N 300010
using namespace std;
int n, m;
int a[N], b[N];
int32_t main(){
ios::sync_with_stdio(false); cin.tie(0);
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 = 0, r = (int) 2e18;
while(l < r){
int mid = (l+r) >> 1;
int res = 0;
// cout << l << " " << r << "\n";
for(int i = 1;i <= n;i++){
int aux = mid;
if(a[i] > b[i]){
if(a[i]*m < aux){
aux -= a[i]*m;
res += m;
}
else{
int t = (aux + a[i] - 1)/a[i];
res += t;
if(res > n*m){r = mid; break;}
continue;
}
}
int t = (aux + b[i] - 1)/b[i];
res += t;
if(res > n*m){r = mid; break;}
}
if(res <= n*m){
l = mid+1;
}
}
l--;
cout << l << "\n";
return 0;
}
