#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;                                                  
         if(C <= 0){                                              
            printf("Yes");                                        
            break;                                                
         }                                                        
         A -= D;                                                  
         if(A <= 0){                                              
            printf("No");                                         
            break;                                                
         }                                                        
      }                                                           
   return 0;                                                      
}   