#include <bits/stdc++.h>
#define rep(a,n) for (ll a = 0; a < (n); ++a)
using namespace std;
typedef long long ll;
using ll = long long;
typedef pair<ll,ll> P;
typedef pair<P,ll> PP;
using Graph = vector<vector<ll> >;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1e18;

//input
ll n;

ll katawa(ll x){
    ll res = 0;
    while(x>0){
        res += x%10;
        x/=10;
    }
    return res;
}
int main(){
    cin >> n;
    rep(i,99){
        n = katawa(n);
    }
    cout << n << endl;

    return 0;
}