#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int main(){
    ll N, M, X, Y;
    while(cin >> N >> M >> X >> Y){
        --X;
        --Y;
        ll a = X % (2 * M), b = Y % (2 * M);
        if(a >= M)a = 2 * M - 1 - a;
        if(b >= M)b = 2 * M - 1 - b;
        puts(a == b ? "YES" : "NO");
    }
}