public static void main ( String args [ ] ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int winner [ ] = new int [ n ] ;
  int loser [ ] = new int [ n ] ;
  int spectator [ ] = new int [ n ] ;
  boolean flag = true ;
  int first = 1 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    winner [ i ] = sc . nextInt ( ) ;
  }
  spectator [ 0 ] = 3 ;
  loser [ 0 ] = winner [ 0 ] == 1 ? 2 : 1 ;
  for ( int i = 0 ;
  i < n - 1 ;
  i ++ ) {
    if ( winner [ i ] != winner [ i + 1 ] ) {
      loser [ i + 1 ] = winner [ i ] ;
      spectator [ i + 1 ] = loser [ i ] ;
    }
    else {
      spectator [ i + 1 ] = loser [ i ] ;
      loser [ i + 1 ] = spectator [ i ] ;
    }
    if ( ( spectator [ i + 1 ] == winner [ i + 1 ] ) || ( winner [ 0 ] == 3 ) ) flag = false ;
  }
  if ( flag && winner [ 0 ] != 3 ) System . out . println ( "YES" ) ;
  else System . out . println ( "NO" ) ;
}

public static void main ( String args [ ] ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int winner [ ] = new int [ n ] ; int loser [ ] = new int [ n ] ; int spectator [ ] = new int [ n ] ; boolean flag = true ; int first = 1 ; for ( int i = 0 ; i < n ; i ++ ) { winner [ i ] = sc . nextInt ( ) ; } spectator [ 0 ] = 3 ; loser [ 0 ] = winner [ 0 ] == 1 ? 2 : 1 ; for ( int i = 0 ; i < n - 1 ; i ++ ) { if ( winner [ i ] != winner [ i + 1 ] ) { loser [ i + 1 ] = winner [ i ] ; spectator [ i + 1 ] = loser [ i ] ; } else { spectator [ i + 1 ] = loser [ i ] ; loser [ i + 1 ] = spectator [ i ] ; } if ( ( spectator [ i + 1 ] == winner [ i + 1 ] ) || ( winner [ 0 ] == 3 ) ) flag = false ; } if ( flag && winner [ 0 ] != 3 ) System . out . println ( " YES " ) ; else System . out . println ( " NO " ) ; }
(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)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) dimensions: (dimensions) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) dimensions: (dimensions) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) dimensions: (dimensions) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (local_variable_declaration type: (boolean_type) declarator: (variable_declarator name: (identifier) value: (true))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (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 (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (decimal_integer_literal))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (ternary_expression condition: (binary_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (decimal_integer_literal)) consequence: (decimal_integer_literal) alternative: (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: (binary_expression left: (identifier) right: (decimal_integer_literal))) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) consequence: (block (expression_statement (assignment_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (array_access array: (identifier) index: (identifier)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (array_access array: (identifier) index: (identifier))))) alternative: (block (expression_statement (assignment_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (array_access array: (identifier) index: (identifier)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (array_access array: (identifier) index: (identifier)))))) (if_statement condition: (parenthesized_expression (binary_expression left: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) right: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (decimal_integer_literal))))) consequence: (expression_statement (assignment_expression left: (identifier) right: (false)))))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (binary_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) 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)))))))