#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define rrep(i,n) for(int i=1;i<(n);++i)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define maxs(a, b) a = max(a, b)
#define mins(a, b) a = min(a, b)
using namespace std;
template<class T> inline istream& operator >> (istream & c, vector<T> & A) {rep(i, A.size()) c >> A[i];return c;}
typedef long long ll;
typedef pair<int, int> P;
const ll linf = (1ll << 61);
const int inf = 1001001001;
const int mod = 1000000007;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	long long n;
	cin >> n;
	auto keta_sum = [&](long long a) {
		int ret = 0;
		while (a) ret += (a % 10), a /= 10;
		return ret;
	};
	rep(i, 100) {
		n = keta_sum(n);
	}
	cout << n << endl;
	return 0;
}