#include <stdio.h>
 
int main(void) {
    int a, b, c, d, X, Y;
    scanf("%d %d %d %d", &a, &b, &c, &d);
  	X = a / d;
  	Y = c / b;
 	if (X > Y){
      printf("Yes");
    }else if((X == Y) && (a % d > 0)){
      printf("Yes");
    }else{
      printf("No");
    }
    return 0;
}