/* -*- coding: utf-8 -*-
 *
 * 1168.cc:  No.1168 Digit Sum Sequence - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

int digsum(int n) {
  int sum = 0;
  while (n > 0) {
    sum += n % 10;
    n /= 10;
  }
  return sum;
}

/* main */

int main() {
  int n;
  scanf("%d", &n);

  for (;;) {
    int s = digsum(n);
    if (s == n) break;
    n = s;
  }

  printf("%d\n", n);
  return 0;
}