汉罗塔问题

a=0
def hanoi(n,src,dst,mid):
global a
if n==1:
print("{}:{}->{}".format(1,src,dst))
a+=1
else:
hanoi(n-1,src,mid,dst)
print("{}:{}->{}".format(n,src,dst))
a+=1
hanoi(n-1,mid,dst,src)
n=eval(input())
hanoi(n,"A","C","B")
print(a)