#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const string YES = "Yes";
const string NO = "No";

void solve(long long A, long long B, long long C, long long D){
    int win1 = C/B;
    int win2 = A/D;
    if(C%B!=0){
        win1++;
    }
    if(D%A!=0){
        win2++;
    }
    if(win1<=win2){
        cout <<YES<< endl;
    }else{
        cout <<NO <<endl;
    }

}

int main(){
    long long A;
    scanf("%lld",&A);
    long long B;
    scanf("%lld",&B);
    long long C;
    scanf("%lld",&C);
    long long D;
    scanf("%lld",&D);
    solve(A, B, C, D);
    return 0;
}
