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

a = []
for z in [X-1, Y-1]:
    if (z//M) % 2 == 0:
        a.append(z%M)
    else:
        a.append((M-1)-z%M)

if a[0] == a[1]:
    print('YES')
else:
    print('NO')