#include <stdio.h>

int main()
{
	int x,y,z,t;
	int i = 1;
	int dam = 0;
	
	scanf("%d\n", &x);
	scanf("%d\n", &y);
	scanf("%d\n", &z);
	scanf("%d\n", &t);
	x = (2 << x);
	dam = z - t;
	i = 0;
	while((y != 0) || (y > x)){
		y += dam;
		i++;
	}
	printf("%d", i);
	return (0);
}