#include <iostream>
using namespace std;
unsigned int calculateTriangleNum(unsigned int n);
int main(){
unsigned int n;
cin >> n;
cout << calculateTriangleNum(n) << endl;
return 0;
}
unsigned int calculateTriangleNum(unsigned int n) {
if(n==0)
{
return 0;
}
else if(n==1)
{
return 1;
}
else
{
return (n % 10 + calculateTriangleNum(n / 10));
}
}
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