#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h> 
#include <complex>
#include <queue>
#include <set>
#include <unordered_set>
#include <list>
#include <chrono>
#include <random>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <map>
#include <unordered_map>
#include <stack>
#include <iomanip>
#include <fstream>
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pl;
typedef pair<double,double> pdd;
typedef vector<ll> vi;
typedef vector<vector<int> > vv32;
typedef vector<vector<ll> > vv64;
typedef vector<vector<pl> > vvp64;
typedef vector<pl> vp64;
ll MOD = 998244353;
double eps = 1e-12;
#define forq(i,e) for(ll i = 0; i < e; i++)
#define fors(i,s,e) for(ll i = s; i < e; i++)
#define rforn(i,s) for(ll i = s; i >= 0; i--)
#define rforsn(i,s,e) for(ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout<<#x<<" = "<<x<<ln
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define INF 2e18
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())
#define MXE(a) *max_element(all(a))
#define MNE(a) *min_element(all(a))
#define sort1(a) sort(all(a))
#define rev(a) reverse(all(a))
#define revsort(a) sort(all(a),greater<>())
//*****bitset section**********
#define cset(x) __builtin_popcountll(x)
#define pairty(x) __builtin_parityll(x)
#define lz(x) __builtin_clzll(x)
#define tz(x) __builtin_ctzll(x)
 

void solve(){
}
int main()
{
 fast_cin();
 ll t;
cin>>t;
ll sum=0;
ll r=t;
while(r>9){

while(t>0){
    sum+=t%10;
    t/=10;
  //  cout<<t;
}
r=sum;
t=sum;
sum=0;
}
cout<<t<<"\n";
 return 0;
}