#include <iostream>
#include <string>
#include <algorithm>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
int main() {
    string s;
    cin >> s;
    int co = 0;
    for (int i = 0; i < s.size(); i++) {
        co += int(s[i] - '0');
    }
    cout << co % 10 + co / 10 << endl;
    return 0;
}