#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 = c - b;
    if (c > 0) a = a - d;
  }
 
  if (c <= 0)
    printf("Yes\n");
  else
    printf("No\n");
 
  return 0;
}