#include <iostream>
#include <vector>
using namespace std;

int main(void){
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    while(1){
        c-=b;
        if(c<=0){
            cout<<"Yes"<<endl;
            break;
        }
        a-=d;
        if(a<=0){
            cout<<"No"<<endl;
            break;
        }
    }
}