import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt(),b = sc.nextInt(),c = sc.nextInt(),d = sc.nextInt(),e = sc.nextInt();
		int ans = a-b;
		if(d>e)ans += c*(d-e);
		System.out.println(ans);
		sc.close();
	}
}