#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<ll,ll> P;
typedef modint998244353 mint;
#define rep(i,a,b) for(ll i=a;i<b;i++)
#define rrep(i,a,b) for(ll i=a;i>=b;i--)
const ll inf=1e18;
ll n;
ll a[105];
int main(void){
    cin.tie(0);
    ios::sync_with_stdio(0);
    cin>>n;
    a[1]=n;
    rep(i,2,101){
        ll cnt=0;
        ll k=a[i-1];
        while(k>0){
            cnt+=k%10;
            k/=10;
        }
        a[i]=cnt;
    }
    cout<<a[100]<<endl;
}