# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')
from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline

N = int(input())
def f(x):
    X = list(str(x))
    X = [int(i) for i in X]
    return sum(X)
    
tN = N
for i in range(99):
    tN = f(tN)
print(tN)