#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

using namespace std;

int getClass( int rank, int classCount )
{
    int tmp = (int)(rank/classCount);
    int ret = rank - tmp * classCount;
    if( tmp % 2 == 0 )
    {
        // even
    }
    else
    {
        // odd
        // reverse
        ret = classCount - 1 - ret;
    }
    return ret;
}


void solve()
{
    int N,M,X,Y;
    cin >> N >> M;
    cin >> X >> Y;
    
    string ans = "NO";
    
    if( M == 1 )
    {
        ans = "YES";
    }
    else
    {
        int classOfX = getClass(X-1,M);
        int classOfY = getClass(Y-1,M);
        
        if( classOfX == classOfY )
        {
            ans = "YES";
        }
    }
    cout << ans <<endl;
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}