/* -*- coding: utf-8 -*-
 *
 * 2138.cc:  No.2138 Add Bacon - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int INF = 1 << 30;

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int a, b, c, d, e;
  scanf("%d%d%d%d%d", &a, &b, &c, &d, &e);

  int maxh = -INF;
  for (int i = 0; i <= c; i++) {
    int h = (a + d * i) - (b + e * i);
    maxh = max(maxh, h);
  }

  printf("%d\n", maxh);
  return 0;
}