#class change
N,M=(int(i) for i in input().split())
X,Y=(int(i) for i in input().split())
def c(nu,cl):
    cy=nu//cl
    nu%=cl
  #  if nu==0:
    #    nu+=cl
    if cy%2==1:
        nu*=-1
        nu+=cl+1
        if nu>cl:
           nu=cl
    return nu
if c(X,M)==c(Y,M):
    print("YES")
else:
    print("NO")