#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(LL i = a;i<b; i++)
#define rrep(i,a,b) for(LL i = a;i>=b; i--)
#define INF ((1LL<<62)-(1LL<<31))
#define ooki 9,223,372,036,854,775,807
#define tii -9,223,372,036,854,775,808
typedef long long LL;
int main(){
 int n,sum=0;
  cin >> n;
  rep(i,0,100){
   while(n>0){
    sum+=n%10;
     n/=10;
   }
   n=sum;
   sum=0;
  }
  cout<<n<<endl;

}