#54746: C++ 遞迴解
xutingyao0505@gmail.com
(TingYao Xu)
#include <bits/stdc++.h>
using namespace std;
int sum_digit(long long num) {
int total = 0;
if (num < 10) return num;
while (num > 0) {
total += num % 10;
num /= 10;
}
return sum_digit(total);
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
long long num;
int result = 0;
while (cin >> num && num != 0){
result = sum_digit(num);
cout << result << endl;
}
return 0;
}