#include<stdio.h>

int main()
{
	int X, Y, N;
	double c;

	while(scanf("%d %d %d %lf", &X, &Y, &N, &c),N)
	{
		c/= 1200.0;
		++c;
		double dpt = X;
		N*=12;
		for(int i=1; i<=N;i++)
		{
			if ((dpt = dpt * c - Y) < 0)
				break;
		}
		if (dpt < 0)
			puts("YES");
		else
			puts("NO");
	}
	
	return 0;
}