#include<bits/stdc++.h>
using namespace std;

typedef long long int ll;
typedef pair<ll,ll> P;

int main(){
    int ahp,aat,chp,cat;
    cin>>ahp>>aat>>chp>>cat;
    while(ahp*chp>0){
        chp-=aat;
        if(chp<=0)break;
        ahp-=cat;
        if(ahp<=0)break;
    }
    if(ahp<=0){cout<<"No";}
    else{cout<<"Yes";}


    return 0;
}