#include <bits/stdc++.h> using namespace std; #define int long long signed main() { ios::sync_with_stdio(0); cin.tie(NULL), cout.tie(NULL); int n, m; cin>>n>>m; 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]; int s=0, e=1e18; while (s+1<e) { int mid=(s+e)/2; int su=0; for (int i=0;i<n;i++) if (max(a[i],b[i])*m>=mid) su-=m-(mid+max(a[i],b[i])-1)/max(a[i],b[i]); else su+=(mid-max(a[i],b[i])*m+b[i]-1)/b[i]; if (su<=0) s=mid; else e=mid; } cout<<s<<endl; return 0; }