#include <iostream>

using namespace std;
int sumac (int n)
{
    int s=0;
    while (n>0)
    {
        s=s+n%10;
        n=n/10;
    }
    return s;
}
int f(long long n)
{
    while (n>9)
    {
        n=sumac(n);
    }
    return n;
}
int main()
{
    long long n;
    cin>>n;
    cout<<f(n);
    return 0;
}