#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

int solve(int a, int m)
{
    -- a;
    if(a / m % 2 == 0)
        return a % m + 1;
    else
        return m - a % m;
}

int main()
{
    int n, m, x, y;
    cin >> n >> m >> x >> y;

    if(solve(x, m) == solve(y, m))
        cout << "YES" << endl;
    else
        cout << "NO" << endl;

    return 0;
}