public static void main ( String [ ] args ) throws IOException {
  BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ;
  String [ ] nm = br . readLine ( ) . split ( " " ) ;
  int n = Integer . parseInt ( nm [ 0 ] ) ;
  int m = Integer . parseInt ( nm [ 1 ] ) ;
  int count = 0 , min_x = m + 1 , max_x = - 1 , min_y = n + 1 , max_y = - 1 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    String [ ] row = br . readLine ( ) . split ( "" ) ;
    for ( int j = 0 ;
    j < m ;
    j ++ ) {
      if ( row [ j ] . contentEquals ( "X" ) ) {
        min_x = Math . min ( min_x , j ) ;
        max_x = Math . max ( max_x , j ) ;
        min_y = Math . min ( min_y , i ) ;
        max_y = Math . max ( max_y , i ) ;
        count ++ ;
      }
    }
  }
  System . out . println ( ( ( max_x - min_x + 1 ) * ( max_y - min_y + 1 ) == count ) ? "YES" : "NO" ) ;
}

public static void main ( String [ ] args ) throws IOException { BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ; String [ ] nm = br . readLine ( ) . split ( " ▁ " ) ; int n = Integer . parseInt ( nm [ 0 ] ) ; int m = Integer . parseInt ( nm [ 1 ] ) ; int count = 0 , min_x = m + 1 , max_x = - 1 , min_y = n + 1 , max_y = - 1 ; for ( int i = 0 ; i < n ; i ++ ) { String [ ] row = br . readLine ( ) . split ( " " ) ; for ( int j = 0 ; j < m ; j ++ ) { if ( row [ j ] . contentEquals ( " X " ) ) { min_x = Math . min ( min_x , j ) ; max_x = Math . max ( max_x , j ) ; min_y = Math . min ( min_y , i ) ; max_y = Math . max ( max_y , i ) ; count ++ ; } } } System . out . println ( ( ( max_x - min_x + 1 ) * ( max_y - min_y + 1 ) == count ) ? " YES " : " 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 (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))))) (local_variable_declaration type: (array_type element: (type_identifier) 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 (string_literal))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (decimal_integer_literal)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (decimal_integer_literal)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal)) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (decimal_integer_literal))) declarator: (variable_declarator name: (identifier) value: (unary_expression operand: (decimal_integer_literal))) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (decimal_integer_literal))) declarator: (variable_declarator name: (identifier) value: (unary_expression operand: (decimal_integer_literal)))) (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: (array_type element: (type_identifier) 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 (string_literal))))) (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 (if_statement condition: (parenthesized_expression (method_invocation object: (array_access array: (identifier) index: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier))))) (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier))))) (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier))))) (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier))))) (expression_statement (update_expression (identifier))))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (ternary_expression condition: (parenthesized_expression (binary_expression left: (binary_expression left: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (identifier)) right: (decimal_integer_literal))) right: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (identifier)) right: (decimal_integer_literal)))) right: (identifier))) consequence: (string_literal) alternative: (string_literal)))))))