#include <iostream>
#include <string>
#include <string.h>
using namespace std;
int main()
{
	string S;
	cin>>S;
	int A=0;
	int i;
	for (int i=1;i<=100;i++){
		A=0;
		for (int j=0;j<S.size();j++){
			A+=S[j]-'0';
		}
		if (A<10){
			cout<<A<<endl;
			return 0;
		}
		char S1[100];
		sprintf(S1,"%lld",A);
		S=S1;
	}
	return 0;
}