public static void main ( String [ ] args ) throws IOException {
  FastScanner input = new FastScanner ( ) ;
  int n = input . nextInt ( ) ;
  int m = input . nextInt ( ) ;
  TreeSet < String > set = new TreeSet < > ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    String s = input . next ( ) ;
    if ( s . contains ( "X" ) ) set . add ( s ) ;
  }
  if ( set . size ( ) == 1 ) System . out . println ( "YES" ) ;
  else System . out . println ( "NO" ) ;
}

public static void main ( String [ ] args ) throws IOException { FastScanner input = new FastScanner ( ) ; int n = input . nextInt ( ) ; int m = input . nextInt ( ) ; TreeSet < String > set = new TreeSet < > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { String s = input . next ( ) ; if ( s . contains ( " X " ) ) set . add ( s ) ; } if ( set . size ( ) == 1 ) System . out . println ( " YES " ) ; else System . out . println ( " NO " ) ; }
(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)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (generic_type (type_identifier) (type_arguments (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments)) arguments: (argument_list)))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (if_statement condition: (parenthesized_expression (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (string_literal)))) consequence: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (decimal_integer_literal))) consequence: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) alternative: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))))))