#include <iostream>
using namespace std;
int main(){
int a,b,c,d;
int f=0;
cin >>a >>b >>c >>d;//体力a,c
while(true){
    c=c-b;//takahashiの攻撃
    if(c<=0){
        f=2; //a win 
        break;
    }
   a=a-d;//aokiの攻撃
    if(a<=0 ){
        f=1; //c win 
        break;
    }
}
if(f==2)cout <<"Yes" <<endl;
else if(f==1)cout <<"No"<<endl;
return 0;
}