#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
typedef long long LL;
LL n;
string s;
int main()
{
cin >> s;
for(int i = 0; i < s.size(); i ++) n += (s[i] - '0');
int ans;
while(n >= 10)
{
ans = 0;
while(n != 0)
{
ans += n % 10;
n /= 10;
}
n = ans;
}
cout << ans;
return 0;
}