#include<stdio.h>
int main()
{
    int a,b,c,d;
    scanf("%d%d%d%d",&a,&b,&c,&d);
    int i=1;
    while(1)
    {
        c=c-b;
         a=a-d;
        if(c<=0){printf("Yes");
            break;}
 
  else if(a<=0){printf("No");
            break;}
    
        i++;
      
    }
    
 
    return 0;
}