#include <bits/stdc++.h>
using namespace std;

#define int long long
#define rep(i,l,r) for(int i=(int)(l);i<(int)(r);i++)
#define all(x) (x).begin(),(x).end()
#define pb push_back
template<class T>bool chmax(T &a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T &a,T b){if(a>b){a=b;return 1;}return 0;}

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;

const int inf = 1LL<<60;
const int mod = 1e9 + 7;
const double eps = 1e-9;

/*{
}*/

int f(int m, int x)
{
  x--;
  int q = x/m;
  int r = x%m;
  if(q%2 == 1) r = m-r-1;
  return r+1;
}

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

  cout << (f(m, x) == f(m, y) ? "YES" : "NO") << endl;

  return 0;
}