#include <stdio.h>
int main(){
  int a, b, c, d;
  scanf("%d %d %d %d", &a, &b, &c, &d);
  while(true){
    c -= b;
    if(b <= 0){
      printf("Yes\n");
      break
    }
    a -= d;
    if(a <= 0){
      printf("No\n");
      break
    }
  }
}
