#include "bits/stdc++.h"
using namespace std;

// コンテスト中のみ
#define int long long

#define ll long long
#define rep(i,n) for(int i = 0; i < (n); i++)
#define P pair<ll,ll>
int MOD = 1000000007;
const ll INF = 1LL << 60;


signed main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	vector<int>a(100);
	a[0] = n;
	rep(i, 100) {
		if (i == 0)continue;
		string tmp = to_string(a[i - 1]);
		int now = 0;
		rep(j, tmp.size())now += tmp[j] - '0';
		a[i] = now;
	}
	cout << a[99] << endl;
	return 0;
}