#include <stdio.h>

int main(void) {

  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;
  }
  printf(a > c ? "Yes" : "No");
  puts("");
  
  return 0;
}