#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
using ll = long long;
using P = pair<int,int>;
ll gcd(ll a, ll b) { return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}




int main()
{
    int A,B,C,D;
    cin >> A >> B >> C >> D;

    string S;
    while(A > 0 || C > 0){
        C = C - B;
        if(C <= 0){
            S = "Yes";
            break;
        }
        A = A - D;
        if(A <= 0){
            S = "No";
            break;
        }
    }

    cout << S << endl;

    return 0;
}
//Ctrl+Shift+Bでコンパイルと実行を行ってデバッグすること