gistfile1.txt

l = 'XYZ'    

def pandovan(n):
    p = []
    for i in range(0,n):
        if i<3:
            p.append(l[i])
        else:
            p.append(p[i-2] + p[i-3])
    str = p[n-2] + p[n-3]
    print str

pandovan(6)