#include<bits/stdc++.h>
#define rep(i, x) for(ll i = 0; i < x; i++)
#define rep2(i, x) for(ll i = 1; i <= x; i++)
#define all(a) (a).begin(),(a).end()
using ll = long long;
using ld = long double;
using namespace std;
ll keta(ll n) {
	ll res = 0;
	while (n >= 1) { res += n % 10; n /= 10; }
	return res;
}

signed main() {
	ll n; cin >> n;
	rep(i, 100) { n = keta(n); }
	cout << n << endl;
	return 0;
}