/* example program to illustrate all the syntax:

   { n = read;
     if n < 0 then
       print "bad"
     else
     { f = 1;
       i = 1;
       while i <= n do
       { f = f * i;
         i = i + 1 }
       print f } }

  next_symbol performs lexical analysis, returning a string that represents
  the next lexeme in the input. To simplify future tasks, some lexemes are
  decorated with an extra first character:
    numbers start with #
    reserved words (if, while, etc) begin with @
    strings begin with " but do not have a " at the end
    @eof represents end of file (on keyboard type ctrl-D)
    @bad represents an incorrect lexeme
    everything else is left as it is

  in this language
    := is used for assignment and == for equality test
    <> (less than or greater than) is for inequality test
    and, or, and not are used instead of &&, ||, and !
*/

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

string next_symbol(istream & in)
{ char c;
  while (true)
  { c = in.get();
    if (in.fail())
      return "@eof";
    if (c > ' ')
      break; }

  if (c == '{')
    return "{";
  else if (c == '}')
    return "}";
  else if (c == '(')
    return "(";
  else if (c == ')')
    return ")";
  else if (c == ';')
    return ";";
  else if (c == '+')
    return "+";
  else if (c == '-')
    return "-";
  else if (c == '*')
    return "*";
  else if (c == '/')
    return "/";
  else if (c == '%')
    return "%";

  else if (c == '<')
  { c = in.peek();
    if (c == '=')
    { in.get();
      return "<="; }
    else if (c == '>')
    { in.get();
      return "<>"; }
    else
      return "<"; }

  else if (c == '>')
  { c = in.peek();
    if (c == '=')
    { in.get();
      return ">="; }
    else
      return ">"; }

  else if (c == '=')
  { c = in.peek();
    if (c == '=')
    { in.get();
      return "=="; }
    else
      return "@bad"; }

  else if (c == ':')
  { c = in.peek();
    if (c == '=')
    { in.get();
      return ":="; }
    else
      return "@bad"; }

  else if (c == '"')
  { string s = "\"";
    while (true)
    { c = in.get();
      if (in.fail())
        return "@bad";
      if (c == '"')
        break;
      s += c; }
    return s; }

  else if (c >= '0' && c <= '9')
  { string s = "#";
    while (true)
    { s += c;
      c = in.peek();
      if (c < '0' || c > '9')
        break;
      in.get(); }
    return s; }

  else if (c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z')
  { string s = "";
    while (true)
    { if (c >= 'A' && c <= 'Z')
        s += (char)(c -'A' + 'a');
      else
        s += c;
      c = in.peek();
      if (c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' || c == '_')
        in.get();
      else
        break; }
    if (s == "if" || s == "while" || s == "then" || s == "do" || s == "else" ||
        s == "print" || s == "read" || s == "and" || s == "or" || s == "not")
      return string("@") + s;
    else
      return s; }

  else
    return "@bad"; }

int main()
{ string s;
  while (true)
  { s = next_symbol(cin);
    cout << s << "\n";
    if (s == "@eof")
      break; } }