#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {
    long long N,M,X,Y;
    cin >> N >> M >> X >> Y;
    X %= 2*M;
    Y %= 2*M;

    if ( X == 0 ) { X = 2*M; }
    if ( Y == 0 ) { Y = 2*M; }

    X = ( X > M ) ? abs(M+1-X) : abs(M-X);
    Y = ( Y > M ) ? abs(M+1-Y) : abs(M-Y);

    cout << ( X == Y ? "YES" : "NO" ) << endl;

    return 0;
}