#include<bits/stdc++.h>
using namespace std;
int s,x,k,g;
int main()
{
	cin>>x;
    while(x>=10)
	{
    	s=0;
    	while(x)
		{
			g=x%10;
			x=x/10;
			s=s+g;
		}
		x=s;
	}
    cout<<x;   
}