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

using ll = long long;
using P = pair<ll, ll>;

const ll MOD = 1e9+7;
// const ll MOD = 998244353;
const ll INF = 1ll<<60;

#define FOR(i,a,b) for (ll i=(a);i<(ll)(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define DEBUG(x) ;
#define DEBUG(x) std::cerr << #x << " : " << (x) << std::endl;

int dx[4]{0, 1, 0, -1};
int dy[4]{1, 0, -1, 0};

ll N;

int main(int argc, char **argv)
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	cin >> N;
	for (ll i = 0; i < 100; ++i)
	{
		auto s = to_string(N);
		ll sum{0};
		for (auto &e : s)
			sum += e - '0';
		N = sum;
	}
	std::cout << N<< std::endl;
	
	return 0;
}