#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(),x.end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
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;}
using ll = long long;

int n,a;

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