N, M = map(int, input().split())
X, Y = map(int, input().split())
SX, MX = (X - 1) // M, (X - 1) % M
SY, MY = (Y - 1) // M, (Y - 1) % M
AX = MX + 1 if SX % 2 == 0 else M - MX
AY = MY + 1 if SY % 2 == 0 else M - MY
print("YES" if AX == AY else "NO")