#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < n; i++)
#define srep(i,a,b) for(int i = a; i < b; i++)
#define all(A) (A).begin(),A.end()
#define MOD 1000000007
using namespace std;
using ll = long long;
using P = pair<char,int>;
using Graph = vector<vector<int>>;

int digit_sum(int x){
	int t = 0;
	while(x){
		t += x%10;
		x /= 10;
	}
	return t;
}

int main(void){
	int n; cin >> n;
	vector<int> A(110); A[0] = n;
	rep(i,100) A[i+1] = digit_sum(A[i]);
	cout << A[99];
}