#include <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define all(a) (a).begin(),(a).end()

typedef long long ll;
typedef pair<int, int> Pii;
typedef tuple<int, int, int> TUPLE;
typedef vector<int> V;
typedef vector<V> VV;
typedef vector<VV> VVV;
typedef vector<vector<int>> Graph;
const int inf = 1e9;
const int mod = 1e9 + 7;

int n, m;

int f(int x) {
    x--;
    x %= 2 * m;
    if (x < m) return x % m;
    return m - 1 - (x % m);
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    cin >> n >> m;
    int x, y;
    cin >> x >> y;
    x = f(x);
    y = f(y);
    // cout << x << " " << y << endl;
    cout << (x == y ? "YES" : "NO") << endl;

}