#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <algorithm>
#include <vector>
 
using namespace std;
 
long long int tong(string s)
{
	long long int ans = 0;
	for (int i = 0; i < s.size(); i++)
	{
		ans += s[i] - '0';
	}
	return ans;
}
 
string chuyen(long long so)
{
	return to_string(so);
}
 
int main(void)
{
	string s;
	cin >> s;
	while (s.size() > 1)
	{
		long long int res = tong(s);
		s = chuyen(res);
	}
	cout << s;
	return 0;
}

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MTIzMTIz

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