#include <stdio.h>

int main(void){

  int a,b,c,d;
  scanf("%d %d %d %d", &a, &b, &c, &d);
  while (1) {
    c -= b;
    if (c <= 0) {
      printf("Yes\n");
      break;
    }
    a -= d;
    if (a <= 0) {
      printf("No\n");
      break;
    }
  }

  return 0;
}