#include<bits/stdc++.h>
using namespace std;
using ll=long long;

int main(){
  ll A,B,C,D,E;
  cin>>A>>B>>C>>D>>E;
  ll ans=A-B;
  for(ll i=0;i<C;i++){
    A+=D;
    B+=E;
    ans=max(ans,A-B);
  }
  cout<<ans<<endl;
}