N = int(input())

def fun(N):
    for i in range(10):
        if N % (10**i) != N:
            x = i+1
    a = 0
    c = 0
    for j in range(1,x+1):
        a = int(((N-a) % (10**j)) / 10**(j-1))
        b = a
        c = b + c
    #print(c)    
    return c     

if N < 10:
    print(N)

if fun(N) > 10:
    print(fun(fun(N)) )