N, M = [int(t) for t in input().split(' ')]
X, Y = [int(t)-1 for t in input().split(' ')]

x = X % M
y = Y % M
if (X // M) & 1 == 1:
    x = M - 1 - x
if (Y // M) & 1 == 1:
    y = M - 1 - y

if x == y:
    print('YES')
else:
    print('NO')