#include <iostream>
using namespace std;
int main(){
  int a,b,c,d,e;cin>>a>>b>>c>>d>>e;
  int nw = d;
  int ret = 0;
  for(int i = 1; (b-c)*a >= i; i++){
    if(i==1){
      ret = d;
      continue;
    }
    if(!(i%10) && e <= nw){
      nw -= e;
    }
    ret += nw;
  }
  cout << ret << endl;
}