#include <stdio.h>
#include <iostream>
#include <vector>

using namespace std;

int main() {
  int A, B, C, D, E; cin >> A >> B >> C >> D >> E;

  B -= C;
  
  int ans = 0;
  int val = D;

  for (int i = 0; i < A * B; i++) {
    ans += val;

    if ((i + 1) % 10 == 0 && E <= val) {
      val -= E;
    }
  }

  cout << ans << endl;
  
  return 0;
}