#include<stdio.h>

int main(void){

	int A, B, C, D, cntt, cnta;

	scanf("%d %d %d %d", &A, &B, &C, &D);

	for(cntt = 0; A > 0 ;){
		A = A - D;
		cntt++;
	}

	for(cnta = 0; C > 0 ;){
		C = C - B;
		cnta++;
	}

	if(cntt >= cnta)
		printf("Yes");
	else
		printf("No");

	return 0;

}