#include <stdio.h>

int main() {
  int a,b,c,d;
  scanf("%d %d %d %d", &a, &b, &c, &d);
  
  while (a > 0 && c > 0) {
  c -= b;
  if (c <= 0)
    break;
  a -= d;
  }
  
  if (a > 0)
    printf("Yes");
  else
    printf("No");
  
  return (0);
}