Mine

class IterQuersumme {    public static void main(String[] arg) {    int qsumme = 0, n = In.readInt();    do {      while (n > 0) {        qsumme += (n % 10);        n = n / 10;      }      n=qsumme;      qsumme=0;    } while (n >= 10);    Out.println(n);  }}