#include <bits/stdc++.h>
using namespace std;

using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define rep2(i, x, n) for(int i = x; i < (n); i++)
#define all(n) begin(n), end(n)
const int INF = 1e9;
const long long llINF = 1LL << 60;
 
int dy[] = {0, 0, 1, -1};
int dx[] = {1, -1, 0, 0};

void Main() {
    int n;
    cin >> n;
    rep(i, 99) {
        int sum = 0;
        string s = to_string(n);
        rep(i, s.size()) {
            sum += s[i] - '0';
        }
        n = sum;
    }
    cout << n << endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(15);
    Main();
    return 0;
}