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

MX,MY = X%(2*M),Y%(2*M)

if X > M:
  MX = M-MX%M+1
if Y > M:
  MY = M-MY%M+1

if MX == MY:
  ans = "YES"
else:
  ans = "NO"

print(ans)