#include<bits/stdc++.h>
using namespace std;
int main(){
    int A,B,C,D,E; cin>>A>>B>>C>>D>>E;
    int N=A*(B-C);
    if(N/10*E<=D)cout<<(D+(D-N/10*E))*(N/10+1)/2*10-(D-N/10*E)*(9-N%10)-D<<endl;
    else cout<<(D+D%E)*(D/E+1)/2*10+D%E*(N+1-(D/E+1)*10)-D<<endl;
}