#include <stdio.h>
#include <stdlib.h>

int main(void) {
	int A,B,C,D;
	scanf("%d %d %d %d\n",&A,&B,&C,&D);

	while(A>=0 ){
		C = C-B;
		if(C<=0){
			printf("Yes");
			return 0;
		}
		A = A-D;
	}
	printf("No");
	return 0;
}