#include<bits/stdc++.h>
#include<math.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define ll long long
#define mod 1000000007
using namespace std;
int main(){
  int a;
  cin>>a;
  int ans=0;
  rep(i,99){
      ans=0;
      while(a>0){
          ans+=a%10;
          a=a/10;
      }
      a=ans;
  }
cout<<a<<endl;
}