= Digital Roots =
http://acm.zju.edu.cn/show_problem.php?pid=1115
{{{#!cplusplus
/*written by czk*/
#include <stdio.h>
#include <ctype.h>

int main() {
    while(1) {
        int sum = 0;
        char c;
        while(!isdigit(c=getchar()));
        if(c=='0') break;
        while(isdigit(c)) {
            sum+= (c-'0');
            c = getchar();
        }
        while(sum >= 10) {
            int temp = sum;
            sum = 0;
            while(temp>0) {
                sum += temp %10;
                temp /= 10;
            }
        }
        printf("%d\n", sum);
    }
}

}}}