#include <bits/stdc++.h>
using namespace std;
int main(void){
    int a,B,c,x,e,goukei=0;cin >> a >> B >> c >> x >> e;
    int b=B-c;
    
    for(int i=0;i<b*a;i++){
        if(i%10==0 && e<=x){
            x=x-e;
        }
        goukei=goukei+x;
    }
    cout << goukei << endl;
}