#include <queue> 
#include <math.h> 
#include <stack> 
#include <stdio.h>
#include <iostream>
#include <vector> 
#include <iomanip> 
#include <string.h> 
#include <algorithm>
using namespace std;
#define LL long long
const int N = 1e5 + 10; 
const int INF = 0x3f3f3f3f; 
char a[N];
int main()
{
	cin >> a;
	int len = strlen(a);
	int sum = 0;
	for (int i = 0 ; i < len; i++)
	{
		sum +=  (a[i] - '0');
	}
	while(sum >= 10)
	{
		int ans = 0;
		while(sum != 0)
		{
			ans += sum%10;
			sum /= 10;

		}
		sum = ans;
	}
	cout << sum << endl;


}