#include <stdio.h>

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