#include <bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;
typedef long long ll;
typedef pair<int,int>P;

const ll MOD=1000000007;
//~ const int MOD=998244353;
const int INF=0x3f3f3f3f;
const ll INFL=0x3f3f3f3f3f3f3f3f;

int main(){
	int n;cin>>n;
	rep(i,99){
		int a=n,sum=0;
		while(a){
			sum+=a%10;
			a/=10;
		}
		n=sum;
	}
	cout<<n<<endl;
}