#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;
using ll = long long;


int main()
{
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    x--;
    y--;
    x %= m*2;
    y %= m*2;
    if (x >= m) x = 2*m -1 - x;
    if (y >= m) y = 2*m -1 - y;
    cout << ((x == y) ? "YES" : "NO") << endl;
}