#include<bits/stdc++.h>
#define inf  (int)1e18
#define EPS   1e-9
#define MOD 1000000007

#define Pi 3.14159
#define rep(i,a,n) for (int i=a;i<n;i++)
#define repk(i,a,n) for(int i=a;i<=(n);i++)
#define ll  long long
#define F first
#define S second
#define pb push_back
#define eb emplace_back
#define mi map<int,int>
#define vi vector<int>
#define ml map<ll,ll>
#define umap unordered_map
using namespace std;



void sol() {
	int n; cin >> n;
	int a[1005];
	int cnt, k = 0;
	while (n > 10) {
		cnt = 0;
		while (n != 0) {
			a[cnt] = n % 10;
			n /= 10;
			cnt++;
		}
		for (int i = cnt - 1; i >= 0; --i)
			k += a[i];

		n = k;
		k = 0;
	}
	cout << n << '\n';
}

int main() {


	int t = 1;
	// cin >> t;

	while (t--) {
		sol();
	}

	return 0;
}