#include <bits/stdc++.h> #define ll long long #define endl '\n' using namespace std; const int N = 300005; ll a[N+2],b[N+3]; ll n,m; bool ch(ll mid){ ll nd=0,gv=0; for(int i=1;i<=n;i++){ if(b[i]>=a[i]){ ll wan=ceil(float(mid)/b[i]); if(wan==0)wan++; if(wan>m){ nd+=wan-m; } else gv+=m-wan; } } return gv>=nd; } int main(){ ios::sync_with_stdio(0); cin.tie(0); cin>>n>>m; for(int i=0;i<=1;i++){ for(int j=1;j<=n;j++){ if(i)cin>>b[i]; else cin>>a[i]; } } ll r= 1e16,l=1; while(l<=r){ ll mid=l+(r-l)/2; if(ch(mid))l=mid+1; else r=mid-1; } cout<<r; //ll c=ceil(float(18)/5)*(5);cout<<c; } /* 3 3 19 4 5 2 6 2 */