#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<queue>
#include<cmath>
#include<cstdio>
#include<tuple>
#include<bitset>
#include<map>

using namespace std;
#define rep(i,n) for(int i=0;i<n;++i)
#define rep1(i,n) for(int i=1;i<=n;++i)
#define ALL(x) x.begin(),x.end()
using lint=long long;
typedef pair<int,int> P;
const int inf=1000000007;
const int MOD=1000000007;
int f(int x){
  int res=0;
  while(x>0){
    res+=x%10;x/=10;
  }
  return res;
}
signed main(){
  int n;cin>>n;
  rep(i,99){
    n=f(n);
  }
  cout<<n<<"\n";
  return 0;
}