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

using ll = long long;
const ll mod=998244353;
using vll =vector<ll>;
using vvll =vector<vll>;
#define rep(i,n) for(int i=0;i<n;i++)




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

}