#include<iostream>
using namespace std;
long long a,b,c=0,d,e[1000001],f[1000001];
int main(){
	cin>>a;
	b=a;
	while(b>0){
		c+=b%10;
		b/=10;
	}
	if(c==1){
		cout<<10<<endl;
	}
	else{
		cout<<c<<endl;
	}
	return 0;
}