#include <bits/stdc++.h> using namespace std; typedef long long ll; int main(){ ll n, m; cin >> n >> m; ll a[n], b[n]; for (ll i = 0; i < n; i ++) cin >> a[i]; for (ll i = 0; i < n; i ++) cin >> b[i]; for (ll i = 0; i < n; i ++) a[i] = max(a[i], b[i]); ll lo = 0, hi = 2e18; while (hi - lo > 1){ ll mid = (lo + hi) / 2; ll rest = 0, del = 0; for (ll i = 0; i < n; i ++){ ll need = mid / a[i]; if (mid % a[i]) need++; del += min(m, need); if (need > m){ ll rem = mid - a[i] * m; need = rem / b[i]; if (rem % b[i]) need++; rest += need; } } if (del + rest <= n * m) lo = mid; else hi = mid; } cout << lo << endl; }