#include <stdio.h>

int main () {
  int a = 0;
  int b = 0;
  int c = 0;
  int d = 0;
  int e = 0;
  
  int res = 0;
  
  res = scanf("%d", &a);
  res = scanf("%d", &b);
  res = scanf("%d", &c);
  res = scanf("%d", &d);
  res = scanf("%d", &e);
  
  if (d > e) {
    printf("%d\n", a-b+c*(d-e));
  } else {
    printf("%d\n", a-b);
  }
  
  return 0;
}