#include <bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define int long long
#define SZ(s) (int)s.size()
const int N = 1e6 + 5;
const int M = 100000;
void slv() {
int n, m;
cin >> n >> m;
vector <int> a(n+1), b(n+1);
for(int i = 1; i <= n; i++) {
cin >> a[i];
}
for(int i = 1; i <= n; i++) {
cin >> b[i];
}
int l = 0, r = 1e18, k = 1e18;
while(l <= r) {
int md = (l + r) / 2, cnt = 0;
for(int i = 1; i <= n; i++) {
int x = md;
if(a[i] >= b[i]) {
int y = min(m, x / a[i] + (x % a[i] != 0));
cnt += y;
x -= (a[i] * y);
}
if(x >= 0) {
cnt += max(0LL, x / b[i] + (x % b[i] != 0));
}
}
if(cnt <= n * m) {
l = md+1LL;
k = md;
}
else {
r = md-1LL;
}
}
cout << k << '\n';
return;
}
signed main(){
ios::sync_with_stdio(false); cin.tie(nullptr);
int T = 1;
// cin >> T;
while(T--) slv();
return 0;
}
