#include "bits/stdc++.h"
#include <random>
using namespace std; typedef unsigned long long _ulong; typedef long long int lint; typedef pair<lint, lint> plint; typedef pair<double long, double long> pld;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define FOR(i, begin, end) for(lint i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(lint i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define endk '\n'
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
const lint mod = 1e9 + 7, INF = 1e18;
lint dx[8] = { 0, -1, 1, 0, 1, -1, 1, -1 }, dy[8] = { 1, 0, 0, -1, -1, -1, 1, 1 };
typedef pair<double, lint> Pa;

lint N;
int main() {
	cin.tie(0); ios_base::sync_with_stdio(false);
	cin >> N;
	lint curr = N;
	REP(i, 99) {
		lint sum = 0;
		while (curr > 0) {
			sum += curr % 10;
			curr /= 10;
		}
		curr = sum;
	}
	cout << curr << endk;
}