#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 10000000

int main(){
	
	int N;
	cin>>N;
	
	for(int i=0;i<99;i++){
		int n = 0;
		while(N!=0){
			n += N%10;
			N/=10;
		}
		N = n;
	}
	
	cout<<N<<endl;
	
	return 0;
}