def f(x):
    q = x // M
    if q % 2:
        return M - 1 - x % M
    else:
        return x % M
    

N, M = map(int, input().split())
X, Y = map(int, input().split())
X, Y = X - 1, Y - 1
print("YES") if f(X) == f(Y) else print("NO")