#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 if nu==0: nu=cl return nu if c(X,M)==c(Y,M): print("YES") else: print("NO")