let read_int in_ch =
    let is_valid ch = ch >= '0' && ch <= '9' in
    let ioc ch = (int_of_char ch)-(int_of_char '0') in

    let res = ref 0 in
    let tmp = ref '0' in
    try
      while true do
        tmp := (input_char in_ch);
        if (is_valid !tmp) then
          begin
            res := !res * 10 + (ioc !tmp);
          end
        else
          raise Exit;
      done;
      !res;
    with
        Exit -> !res;