Digital Roots

#include <iostream>
#include <algorithm>
#include <cstring>
#include <string>
#include <cmath>
using namespace std;
int test(int x)
{
    int sum=0;
    while(x){
        sum+=x%10;
        x/=10;
    }
    sum+=x;
    return sum;
}
int main()
{
    int n;
    while(cin>>n){
        if(n<10) cout<<n<<endl;
        else{
            while(n>=10){
                n=test(n);
            }
            cout<<n<<endl;
        }
    }
    return 0;
}