#include "bits/stdc++.h"
using namespace std;
#ifdef Nero
#include "Deb.h"
#else
#define deb(...)
#endif
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
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];
}
auto ch = [&](long long mid) -> bool {
long long days = 0;
for (int i = 0; i < n; ++i) {
if (b[i] >= a[i]) {
days += (mid + b[i] - 1) / b[i];
} else {
int t = min((long long) m, (mid + a[i] - 1) / a[i]);
days += t;
if (mid - (long long) a[i] * t > 0) {
days += (mid - (long long) a[i] * t + b[i] - 1) / b[i];
}
}
if (days > (long long) n * m) {
return false;
}
}
return true;
};
long long l = 0, r = 2e18;
while (l < r) {
long long mid = (l + r + 1) / 2;
if (ch(mid)) l = mid;
else r = mid - 1;
}
cout << l << '\n';
return 0;
}
