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

def calculate_class(k, M):
    q = (k - 1) // M
    mod = (k - 1) % M
    if q % 2 == 0:
        return mod + 1
    else:
        return M - mod

c_x = calculate_class(X, M)
c_y = calculate_class(Y, M)

print("YES" if c_x == c_y else "NO")