#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
typedef long long ll;
const int MOD = 998244353;
const ll INF = 4611686018427387903LL;
int main()
{
  int N;
  cin >> N;
  rep(i,99){
    int nx=0;
    while (N>0)
    {
      nx+=N%10;
      N/=10;
    }
    N=nx;
  }
  cout << N << endl;
  return 0;
}