public static void main ( String ar [ ] ) {
  Scanner scan = new Scanner ( System . in ) ;
  int test = scan . nextInt ( ) ;
  while ( test -- > 0 ) {
    int n = Integer . parseInt ( scan . next ( ) ) ;
    String s = scan . next ( ) . trim ( ) ;
    String ch = "1" ;
    if ( s . charAt ( n - 1 ) == '0' ) ch = "0" ;
    while ( n -- > 0 ) System . out . print ( ch ) ;
    System . out . println ( ) ;
  }
}

public static void main ( String ar [ ] ) { Scanner scan = new Scanner ( System . in ) ; int test = scan . nextInt ( ) ; while ( test -- > 0 ) { int n = Integer . parseInt ( scan . next ( ) ) ; String s = scan . next ( ) . trim ( ) ; String ch = "1" ; if ( s . charAt ( n - 1 ) == '0' ) ch = "0" ; while ( n -- > 0 ) System . out . print ( ch ) ; System . out . println ( ) ; } }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier) dimensions: (dimensions))) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (while_statement condition: (parenthesized_expression (binary_expression left: (update_expression (identifier)) right: (decimal_integer_literal))) body: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (local_variable_declaration type: (type_identifier) 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: (type_identifier) declarator: (variable_declarator name: (identifier) value: (string_literal))) (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (character_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (string_literal)))) (while_statement condition: (parenthesized_expression (binary_expression left: (update_expression (identifier)) right: (decimal_integer_literal))) body: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list)))))))