#include <bits/stdc++.h>
using namespace std;
using ch = char;
using ll = long long;
using ld = long double;
using db = double;
using st = string;
using vdb = vector<db>;
using vvdb = vector<vdb>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vd = vector<ld>;
using vvd = vector<vd>;
using vs = vector<st>;
using vvs = vector<vs>;
using vc = vector<ch>;
using vvc = vector<vc>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
const ll mod = 998244353;
const ll MOD = 1000000007;
using vp = vector<pair<ll,ll>>;
#define fi first
#define se second

ll keta(ll a){
  ll ans=0;
  while(a!=0){
    ans+=a%10;
    a/=10;
  }
  return ans;
}

int main(){
  ll N;
  cin>>N;
  vl X(100);
  X[0]=N;
  for(int i=1; i<100; i++){
    X[i]=keta(X[i-1]);
  }
  cout<<X[99]<<endl;
}