#include <stdio.h>

void main(void){
	int a,b,c,d,e;
	scanf("%d %d %d %d %d",&a,&b,&c,&d,&e);
	int happinessDegrees = a - b;
	for(int i = 0;i <= c;i++){
		if(happinessDegrees > (c*d+a) - (c*e+b)){
			break;
		}
		happinessDegrees = (c*d+a) - (c*e+b);
	}
	printf("%d",happinessDegrees);
}