#include<stdio.h>
int main(){
	int A, B, C, D;
	scanf("%d %d %d %d", &A, &B, &C, &D);
	int lifespan_t = A / D + (A % D > 0 ? 1 : 0);
	int lifespan_a = C / B + (C % B > 0 ? 1 : 0); 
	if(lifespan_t >= lifespan_a)
		printf("Yes");
	else
		printf("No");
	return 0;
}