public static void main ( String [ ] args ) throws IOException {
  BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ;
  BufferedWriter bw = new BufferedWriter ( new OutputStreamWriter ( System . out ) ) ;
  char [ ] arr = br . readLine ( ) . toCharArray ( ) ;
  int max = 0 , cur = 0 ;
  for ( char c : arr ) {
    if ( c == 'A' || c == 'T' || c == 'C' || c == 'G' ) {
      max = Math . max ( max , ++ cur ) ;
    }
    else {
      cur = 0 ;
    }
  }
  bw . write ( max + "" ) ;
  bw . close ( ) ;
}

public static void main ( String [ ] args ) throws IOException { BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ; BufferedWriter bw = new BufferedWriter ( new OutputStreamWriter ( System . out ) ) ; char [ ] arr = br . readLine ( ) . toCharArray ( ) ; int max = 0 , cur = 0 ; for ( char c : arr ) { if ( c == ' A ' || c == ' T ' || c == ' C ' || c == ' G ' ) { max = Math . max ( max , ++ cur ) ; } else { cur = 0 ; } } bw . write ( max + " " ) ; bw . close ( ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) (throws (type_identifier)) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal)) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (enhanced_for_statement type: (integral_type) name: (identifier) value: (identifier) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (character_literal)) right: (binary_expression left: (identifier) right: (character_literal))) right: (binary_expression left: (identifier) right: (character_literal))) right: (binary_expression left: (identifier) right: (character_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (update_expression (identifier))))))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (decimal_integer_literal))))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (string_literal))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))