#include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <bitset>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;
typedef long long ll;
typedef pair<int,int> pint;
typedef vector<int> vint;
typedef vector<pint> vpint;
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)

int main(void){
	int n, m; cin >> n >> m;
	int x, y; cin >> x >> y;
	int sh = x / m;
	int ah = x % m;
	int sekih;
	if(sh % 2 == 1){
		if(ah == 0) sekih = m;
		else sekih = m - ah + 1;
	}else{
		sekih = ah + 1;
	}

	int st = y / m;
	int at = y % m;
	int sekit;
	if(st % 2 == 1){
		if(at == 0) sekit = m;
		else sekit = m - at + 1;
	}else{
		sekit = at + 1;
	}

	if(sekit == sekih) printf("YES\n");
	else printf("NO\n");

	return 0;
}