public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int m = sc . nextInt ( ) ;
  int arr [ ] = new int [ m ] ;
  for ( int i = 0 ;
  i < m ;
  i ++ ) {
    arr [ i ] = sc . nextInt ( ) ;
  }
  int count = 0 ;
  Arrays . sort ( arr ) ;
  if ( m == 0 ) {
    System . out . println ( "YES" ) ;
    return ;
  }
  if ( arr [ 0 ] == 1 || arr [ m - 1 ] == n ) {
    System . out . println ( "NO" ) ;
  }
  else {
    for ( int i = 1 ;
    i < m ;
    i ++ ) {
      if ( arr [ i - 1 ] + 1 == arr [ i ] ) {
        count ++ ;
        if ( count == 2 ) {
          System . out . println ( "NO" ) ;
          return ;
        }
      }
      else {
        count = 0 ;
      }
    }
    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 arr [ ] = new int [ m ] ; for ( int i = 0 ; i < m ; i ++ ) { arr [ i ] = sc . nextInt ( ) ; } int count = 0 ; Arrays . sort ( arr ) ; if ( m == 0 ) { System . out . println ( " YES " ) ; return ; } if ( arr [ 0 ] == 1 || arr [ m - 1 ] == n ) { System . out . println ( " NO " ) ; } else { for ( int i = 1 ; i < m ; i ++ ) { if ( arr [ i - 1 ] + 1 == arr [ i ] ) { count ++ ; if ( count == 2 ) { System . out . println ( " NO " ) ; return ; } } else { count = 0 ; } } 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: (integral_type) declarator: (variable_declarator name: (identifier) dimensions: (dimensions) 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)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (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))))) alternative: (block (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 (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: (identifier)))) consequence: (block (expression_statement (update_expression (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)))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (decimal_integer_literal))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))))