#include <iostream>
using namespace std;
int main()
{
int n,number,s;
cout<<"Enter a natural number";
cin>>n;
s=9;
while (n>0)
{
number=s%10;
s+=number;       //s=s+number;
n/=10;         //n=n/10;
}
cout<<s;
getchar();
return 0;
}