N,M=map(int,input().split())
X,Y=map(int,input().split())

alpha=(X-1)%(2*M)
beta=(Y-1)%(2*M)

alpha=min(alpha,(2*M-1)-alpha)
beta=min(beta,(2*M-1)-beta)

if alpha==beta:
    print("YES")
else:
    print("NO")