#include <iostream>
#include <fstream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <cmath>
#include <unordered_map>
#include <map>
#include <queue>
#include <string>
#include <set>
#include <list>
#include <climits>
#include <bitset>
#include <numeric>
#include <cassert>
#include <regex>
using std::cout;
using std::cin;
using std::string;
using std::vector;

int main()
{
    int n, m;
    int x, y;
    cin >> n >> m;
    cin >> x >> y;
    x--;
    y--;
    int x_class, y_class;
    if (x/m % 2 == 0)
    {
        x_class = 1 + x%m;
    }
    else
    {
        x_class = m - x%m;
    }
    if (y/m % 2 == 0)
    {
        y_class = 1 + y%m;
    }
    else
    {
        y_class = m - y%m;
    }
    if (x_class == y_class)
    {
        cout << "YES\n";
    }
    else
    {
        cout << "NO\n";
    }
}