#include <iostream>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <random>
#include <queue>
#include <stack>
#include <bitset>
#include <cassert>
#define int long long
#define double long double
#define rep(i,n) for(int i=0;i<n;i++)
#define srep(i,n,m) for(int i=n;i<m;i++)
#define elif else if
#define pi 3.141592653589793
#define prique priority_queue
constexpr auto mod=1000000007;
using namespace std;
int gcd(int a,int b){
    if(b==0) return a;
    return gcd(b,a%b);
}
int lcm(int a,int b){
    return a*b/gcd(a,b);
}
bool prime(int n){
    int cnt=0;
    for(int i=1;i<=sqrt(n);i++){
        if(n%1==0)cnt++;
    }
    if(cnt!=1) return false;
    else return n!=1;
}
struct UnionFind{
    vector<int> r;
    UnionFind(int N){
        r=vector<int>(N,-1);
    }
    int root(int x){
        if(r[x]<0) return x;
        return r[x]=root(r[x]);
    }
    bool unite(int x,int y){
        x=root(x);
        y=root(y);
        if(x==y) return false;
        if(r[x]>r[y]) swap(x,y);
        r[x]+=r[y];
        r[y]=x;
        return true;
    }
    int size(int x){
        return -r[root(x)];
    }
};
vector<int> v;
int n,m,cnt=0,ans=0,aa[220000],ab[220000];
pair<int,int> pp[220000];
string s,ss[220000];
queue<int> que;
signed main(){
    cin>>s;
    rep(i,s.size()){
        cnt+=s[i]-'0';
    }
    cout<<cnt%10+cnt/10<<endl;
}