#include <stdio.h>

int main(){
	int a, b, c, d;
	scanf("%d %d %d %d", &a, &b, &c, &d);
	int turn = 1;

	while ((0 < a) && (0 < c)){
		if (turn++%2) {
			c -= b;
		}else {
			a -= d;
		}
	}
	if (a > c){
		printf("Yes");
	}else {
		printf("No");
	}
	return (0);
}