#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};

vector<long long> toDigit(ll num)
{
	vector<long long> d;
	while (num)
	{
		d.push_back(num%10);
		num /= 10;
	}
	reverse(d.begin(), d.end());
	return d;
}


ll N;

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

	REP(i, 100)
	{
		auto v = toDigit(N);
		N = accumulate(ALL(v), 0ll);
		if (v.size() == 1) break;
	}
	std::cout << N << std::endl;
	
	return 0;
}