#include <stdio.h>

#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")


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

	printf("%d\n", (d < e) ? a - b : a - b + (d - e) * c);

	return 0;
}