#include <stdio.h>

int main(){
  int A,B,C,D;
  scanf("%d %d %d %d", &A,&B,&C,&D);
  
  A = (A+D-1)/D;
  C = (C+B-1)/B;
  if( A >= C ){
    printf("Yes\n");
  }else{
    printf("No\n");
  }
  return 0;
}