#include <stdio.h>
int main(){
	int A,B,C,D,x,check;
	x = 0;
	scanf("%d %d %d %d",&A,&B,&C,&D);
	if(B<C){
		check = 1;
	}
	while(A > 0 && B > 0 && x + x*C < D){
		A = A - 1;
		B = B - C;
		x++;
	}
	if(check == 1){
	    printf("0");
	}
	else{
		printf("%d",x);
	}
	
}