#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define tezz std::ios::sync_with_stdio(false);std::cout.tie(NULL);std:cin.tie(NULL);
ll ss(ll n){
    ll r=0;
    while(n){
        r+=(n%10);
        n/=10;
    }
       return r;
}
int main() {
    ll n;
    cin>>n;
    ll c=1;
    ll r=0;
    while(c<101)
    {
        c++;
        r=ss(n);
        n=r;
        if(c==101) break;
    }
    cout<<r<<endl;
}