#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

int main(){
    string n;
    cin >> n;
    if(n=="0"){
        cout << 0 << endl;
        return 0;
    }
    int s = 0;
    rep(i,n.size()) s += n[i]-'0';
    s %= 9;
    if(s==0) cout << 9 << endl;
    else cout << s << endl;
    return 0;
}