#include <bits/stdc++.h> using namespace std; int main(){ int a,b=0; cin>>a; while(a>9){ b=0; for(int i=a;i>0;i/=10){ b=b+i%10; } a=b; } cout<<b; return 0; }

#include<bits/stdc++.h>
using namespace std;
int main() {
	int a,b=0;
	cin>>a;
	while(a>9){
		b=0;
		for(int i=a;i>0;i/=10){
			b=b+i%10;
		}
		a=b;
	}
	cout<<b;
	return 0;
}