#include #define FOR(i,a,b) for(int i=(a);i<(b);i++) #define REP(i,b) FOR(i,0,b) #define ALL(c) c.begin(),c.end() #define PB push_back #define TT second.second #define SS second.first #define FF first using namespace std; typedef long double ld; typedef long long LL; typedef double ut; typedef vector VI; typedef pair pr; typedef pair ppr; typedef vector Vpr; typedef priority_queue > PQ; const int INF=1<<30; const int BITSIZE=1<<12; const int SIZE=10+2*1e4; int main(){ LL N,M,X,Y; cin >> N >> M >> X >> Y; M*=2; if(X%M==Y%M || (X%M+Y%M)==M+1) cout << "YES" << endl; else cout << "NO" << endl; return 0; }