#include<bits/stdc++.h>
#define rep(i, n) for (int i=0;i<(n);i++)
using namespace std;
typedef long long ll;
 
int main(void){
    int a, b, c, d;
    cin>>a>>b>>c>>d;
    int now = 0;
    while(a>0&&c>0){
        if(now%2==0){
            c-=b;
        }
        else a-=d;
        now++;
    }
    if(a<=0) cout<<"No"<<endl;
    else cout<<"Yes"<<endl;
    return 0;
}