public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int m = sc . nextInt ( ) ;
  int [ ] dirty = new int [ m ] ;
  for ( int i = 0 ;
  i < m ;
  i ++ ) {
    dirty [ i ] = sc . nextInt ( ) ;
  }
  Arrays . sort ( dirty ) ;
  if ( m == 0 ) {
    System . out . println ( "YES" ) ;
    return ;
  }
  if ( dirty [ 0 ] == 1 || dirty [ m - 1 ] == n ) {
    System . out . println ( "NO" ) ;
    return ;
  }
  for ( int i = 0 ;
  i < m - 2 ;
  i ++ ) {
    if ( dirty [ i ] + 1 == dirty [ i + 1 ] ) {
      if ( dirty [ i + 1 ] + 1 == dirty [ i + 2 ] ) {
        System . out . println ( "NO" ) ;
        return ;
      }
    }
  }
  System . out . println ( "YES" ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int m = sc . nextInt ( ) ; int [ ] dirty = new int [ m ] ; for ( int i = 0 ; i < m ; i ++ ) { dirty [ i ] = sc . nextInt ( ) ; } Arrays . sort ( dirty ) ; if ( m == 0 ) { System . out . println ( " YES " ) ; return ; } if ( dirty [ 0 ] == 1 || dirty [ m - 1 ] == n ) { System . out . println ( " NO " ) ; return ; } for ( int i = 0 ; i < m - 2 ; i ++ ) { if ( dirty [ i ] + 1 == dirty [ i + 1 ] ) { if ( dirty [ i + 1 ] + 1 == dirty [ i + 2 ] ) { System . out . println ( " NO " ) ; return ; } } } System . out . println ( " YES " ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) 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) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (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 (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) (return_statement))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (identifier)))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) (return_statement))) (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: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (decimal_integer_literal)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) (return_statement))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))