#include <iostream>
#include <cstdio>
#include <cassert>
#include <cstring>
#include <vector>
#include <valarray>
#include <array>
#include <queue>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <cmath>
#include <complex>
#include <random>

using namespace std;
using ll = long long;
using ull = unsigned long long;
constexpr int TEN(int n) {return (n==0)?1:10*TEN(n-1);}

int main() {
    int n, m, x, y;
    cin >> n >> m >> x >> y; x--; y--;
    int a = x%(2*m), b = y%(2*m);
    a = min(a, 2*m-1-a);
    b = min(b, 2*m-1-b);
    if (a==b) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
    return 0;
}