#include<iostream>
#include<vector>

using namespace std;

void a(){
    int S,W;
    cin >> S >> W;
    if(W<S){
        cout << "safe"; 
    }
    else{
        cout << "unsafe";
    }
}

void b(){
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    int T = a/d;
    if (a%d!=0)T++;
    int A = c/b;
    if (c%b!=0)A++;
    if(A>T)
    {
        cout << "No";
    }
    else cout << "Yes";
}
int main(void){
    //a();
    b();
}