#include <iostream> using namespace std; #define int long long int a[3<<17], b[3<<17]; signed main(){ int n, m; 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]); int l = 0, r = 1e18; while (l + 1 < r){ int mid = (l + r) / 2; int req = 0; for (int i=1;i<=n;i++){ if (m * a[i] >= mid) req += (mid + a[i] - 1) / a[i]; else req += m + (mid - m * a[i] + b[i] - 1) / b[i]; } if (req <= m * n) l = mid; else r = mid; } cout<<l<<'\n'; }