#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
static const int INF = 0x3f3f3f3f; static const long long INFL = 0x3f3f3f3f3f3f3f3fLL;
typedef vector<int> vi; typedef pair<int, int> pii; typedef vector<pair<int, int> > vpii; typedef long long ll;
template<typename T, typename U> static void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> static void amax(T &x, U y) { if(x < y) x = y; }

int main() {
	int N; int M;
	while(~scanf("%d%d", &N, &M)) {
		int X; int Y;
		scanf("%d%d", &X, &Y), -- X, -- Y;
		auto f = [=](int x) {
			int t = x % (M * 2);
			if(t < M)
				return t;
			else
				return M - 1 - (t - M);
		};
		bool ans = f(X) == f(Y);
		puts(ans ? "YES" : "NO");
	}
	return 0;
}