#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
#include <tuple>
#include <bitset>

using namespace std;

#define int long long

signed main() {
	int h, w, n, k;
	cin >> h >> w >> n >> k;

	//h + w - 1 回順番が回る
	//h + w - 1 回目の人が負け

	int last = (h + w - 1) % n;
	if (last == 0)last = n;

	if (last == k) {
		cout << "YES" << endl;
	}else {
		cout << "NO" << endl;
	}


	return 0;
}