N, M = map(int, input().split())
X, Y = map(int, input().split())
X -= 1
Y -= 1


def calc_class(n):
    sho, amari = divmod(n, M)
    if sho%2 == 0:
        return amari
    else:
        return M - 1 - amari

if calc_class(X) == calc_class(Y):
    print('YES')
else:
    print('NO')