#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 mod = 2 * m;
	int numx = x % mod;
	int numy = y % mod;
	if(numx > m) numx = 2 * m - numx + 1;
	if(numy > m) numy = 2 * m - numy + 1;
	if(numx == numy) printf("YES\n");
	else printf("NO\n");
	return 0;
}