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