#include <stdio.h>

int main(void)
{
	int A, B, C, D;
	int count=0;
	
	scanf("%d, %d, %d, %d", &A, &B, &C, &D);
	
	for(;A<=0 || C<=0;count++)
	{
		if(count%2 == 1)
		{
			A = A - D;
		}
		else
		{
			C = C - B
		}
	}
	
	if(A<=0)
	{
		printf("No\n");
	}
	else
	{
		printf("Yes\n");
	}
	
	return 0;
}