#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;

#define REP(i,s,e) for (i = s; i <= e; i++)
#define rep(i,n) REP (i,0,(int)(n)-1)
#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP (i,(int)(n)-1,0)
#define INF (int)1e8
#define MOD (int)(1e9+7)

typedef long long ll;

int main(void) {
    int h, w;
    ll n, k;
    cin >> h >> w >> n >> k;
    if ((h + w - 2) % n + 1== k)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
    return 0;
}