#include<stdio.h>
int main()
{
	int a, b, c, d, e;
	scanf("%d %d %d %d %d", &a, &b, &c, &d, &e);
	if (d > e)
		printf("%d\n", a - b + c * (d - e));
	else
		printf("%d\n", a - b);
	return 0;
}