#include <bits/stdc++.h> using namespace std; #define int long long int const N=3e5+10; int n,m; int a[N],b[N]; bool check(int vl) { int le=n*m; int tot=0; for (int i=0;i<n;i++) { int mx=max(a[i],b[i]); int f=(vl+mx-1)/mx; f=min(f,m); int z=max(0ll,vl-f*mx); int g=(z+b[i]-1)/b[i]; le-=(f+g); if (le<0) return 0; } return 1; } inline void solve() { cin>>n>>m; for (int i=0;i<n;i++) cin>>a[i]; for (int i=0;i<n;i++) cin>>b[i]; int st=0,en=3e18+10; while (st+1<en) { int mid=(st+en)/2; if (check(mid)) st=mid; else en=mid; } cout<<st<<endl; } signed main() { ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL); int t=1; // cin>>t; for (int i=1;i<=t;i++) { solve(); } }