#include <bits/stdc++.h>

#define rep(X,N) for(ll X = 0LL; X < (N); X++)
#define ALL(V) (V).begin(),(V).end()
#define endl "\n"

using namespace std;
typedef long long ll;

const double PI = 3.1415926535897932384626;
const ll MODN = 1000000007;
const ll MODN2 = 998244353;
const double EPS = 1e-10;

int digitsum(int n){
    int result = 0;

    while(n > 0){
        result += n % 10;
        n = n / 10;
    }

    return result;
}

int main(){

    vector<int> v(100);
    cin >> v[0];

    rep(i, 99){
        v[i + 1] = digitsum(v[i]);
    }

    cout << v[99] << endl;

    return 0;
}