#include<stdio.h>
int main() 
{
  int A, B, C, D;
  scanf("%d", &A) ;
  scanf("%d", &B) ;
  scanf("%d", &C) ;
  scanf("%d", &D) ;
  if((A>=1||A<=100) &&(B>=1||B<=100) &&(C>=1||C<=100) &&(D>=1||D<=100)) 
  {
    do
    {
      C=D-B;
      A=B-D;
      if(A<=0) 
      {printf("no") ;
       exit (0) ;
      }
      else(C<=0) {printf("yes"};
                  }while(A>=C) 
                         }
                         }
  