#include "bits/stdc++.h"
using namespace std;
#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif
const int maxn = 3e5 + 5;
int n, m, a[maxn], b[maxn];
bool check(long long mid) {
long long cnt = 0;
for (int i = 1; i <= n; ++i) {
if (1ll * a[i] * m >= mid) {
long long x = (1ll * a[i] * m - mid) / a[i];
cnt += x;
}
}
for (int i = 1; i <= n; ++i) {
if (1ll * a[i] * m < mid) {
long long need = mid - 1ll * a[i] * m;
need = (need + b[i] - 1) / b[i];
cnt -= need;
}
}
return cnt >= 0;
}
void solve() {
cin >> n >> m;
for (int i = 1; i <= n; ++i) {
cin >> a[i];
}
for (int i = 1; i <= n; ++i) {
cin >> b[i];
a[i] = max(a[i], b[i]);
}
long long l = 0, r = 1e16, res = 0;
while (l <= r) {
long long mid = (l + r) >> 1;
if (check(mid)) {
res = mid;
l = mid + 1;
} else {
r = mid - 1;
}
}
cout << res;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
