#include <bits/stdc++.h>
#include <numeric>
using namespace std;
#define ll long long
#define mod107 1000000007
#define rep(i, n) for (int i = 0; i < n; ++i)
#define Graph vector<vector<int>>;
#define grepq priority_queue<double, std::vector<double>, std::greater<double>>
#define all(v) v.begin(), v.end()
#define PI acos(-1)
#define inf 1000000321
int dx[4] = {0,1,0,-1};
int dy[4] = {1,0,-1,0};


unsigned GetDigit(unsigned num)
{
    return log10(num) + 1;
}

ll dp[100500];

int main(){
    ll N;
    cin >> N;
    for(int i = 0;i < 100;i++){
        ll sum = 0;
        int time = GetDigit(N);
        while(N > 0){
            sum += N%10;
            N/=10;
        }
        N = sum;
    }
    cout << N << endl;
}