public static void main(String[] args) {
    int n = 1;
    double sum = 0.0f;
    System.out.println((double)9/10);
    while (n < 10000) {
      int p = ((n*n)+n)/2;
      if (p%2 == 1) {
        sum += 2*(double)1/(Math.pow(3, n));
      }
      n++;
    }
    System.out.println(sum);
  }