#include <bits/stdc++.h>
#include <atcoder/all>


using namespace std;
using namespace atcoder;
#define rep(i,m,n,k) for (int i = (int)(m); i < (int)(n); i += (int)(k))
#define rrep(i,m,n,k) for (int i = (int)(m); i > (int)(n); i += (int)(k))
#define ll long long
#define list(T,A,N) vector<T> A(N);for(int i=0;i<(int)(N);i++){cin >> A[i];}

const ll mod = 1000000000;
using mint = static_modint<1000000000>;

int main(){
    
    ll H,W,N,K;
    cin >> H >> W >> N >> K;
    if (N==1){
        cout << "YES" << endl;
        return 0;
    }
    if ((H+W-1)%N==K){
        cout << "YES" << endl;
    }
    else{
        cout << "NO" << endl;
    }
    return 0;
}