    #include<stdio.h>
    int main(){
      int A,B,C,D;
      scanf("%d %d %d %d",&A,&B,&C,&D);
      while(A>0&&C>0){
        A=A-D;
        C=C-B;
      }
      if(A>0){
        printf("Yes");
      }
      else{
        printf("No");
      }
      
        
      return(0);
    }