from math import ceil
N,M = map(int,input().split())
X,Y = map(int,input().split())

MX,MY = ceil(X/M),ceil(Y/M)
ans = "NO"

if MX%2 == MY%2 == 0:
  if X%M == Y%M:
    ans = "YES"
elif MX%2 != 0 and MY%2 != 0:
  if X%M == Y%M:
    ans = "YES"
else:
  if X+1 == Y:
    ans = "YES"
  elif X%M == M-Y%M+1:
    ans = "YES"

print(ans)