尾递归解决类斐波那契数列

n = int(input())
def A(i,a,b,c):
    if i ==1:
        return(a)
    elif i == 2:
        return(b)
    elif i == 3:
        return(c)    
    else:
        return A(i-1,b,c,a+2*b+c)
S = A(n,0,1,1)
print(S)