#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <typeinfo>
#include <numeric>
#include <functional>
#include <unordered_map>
#include <bitset>
#include <stack>
#include <assert.h>
#include <unordered_set>
#include <random>


using namespace std;
using ll = long long;
using ull = unsigned long long;

const ll INF = 1e18;
const ll MOD = 1e9 + 7;


#define REP(i, n) for(ll i = 0; i < n; i++)


























int main(){
    ll n;
    cin >> n;
    for(ll i = 2; i <= 100; i++){
        ll s = 0, t = n;
        while(t){
            s += t % 10;
            t /= 10;
        }
        n = s;
    }
    cout << n << endl;
}