#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define ALL(v) (v).begin(), (v).end()
using ll = long long;
constexpr int INF = 1e9;
constexpr long long LINF = 1e18;
constexpr long long MOD = 1e9 + 7;

long long SOD(long long n) {
    long long sum = 0;
    while (n > 0) {
        sum += n % 10;
        n /= 10;
    }
    return sum;
}

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