def calkin(n):
    L=[(1,1)]
    for x in range(1,n+1):
        for i in L:
            yield (L[0]+L[1],L[1])
                yield (L[0],L[0]+L[1])
            L=[(x+y,y) for (x,y) in L]+[(x,x+y) for (x,y) in L]