Could You help me, Guys. I give up.

// That solution works for me. public static void main(String[] args) throws Exception { double sum = 0; int count = 0; double mean; for (int i = 1; ; i++) { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); int num = Integer.parseInt(reader.readLine()); if (num != -1) { count++; sum = sum + num; } else if (num == -1) { mean = sum / count; System.out.println(mean); break; } }

thank you guys. trued your hints. but anyway compiler says all the time "cannot find simbol", and points BufferedReader class. maybe to use Scanner or what?

The reason it doesn't run as expected is because you get the input only once before while code block is executed. You need to put

int number = Integer.parseInt(br.readLine());

inside while block. And as Andason says change variable type of sum from int to double. I don't know how math works in Java but int divide by int will result in int variable type even if you are trying to store it in double.

try changing the sum to type double and make the while block look like double sum = 0.0, count = 0; while(true) { int x = Integer.parseInt(in.readLine()); if(x == -1) break; sum += x; count++; }