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