public static void main ( String arg [ ] ) {
  Scanner sc = new Scanner ( System . in ) ;
  long n = sc . nextInt ( ) ;
  int m = sc . nextInt ( ) ;
  int flag = 0 ;
  long [ ] ar = new long [ m ] ;
  for ( int i = 0 ;
  i < m ;
  i ++ ) {
    ar [ i ] = sc . nextLong ( ) ;
    if ( ar [ i ] == 1 || ar [ i ] == n ) flag = 1 ;
  }
  if ( flag == 1 ) {
    System . out . println ( "NO" ) ;
    System . exit ( 0 ) ;
  }
  Arrays . sort ( ar ) ;
  int count = 1 ;
  for ( int i = 1 ;
  i < m ;
  i ++ ) {
    if ( ar [ i ] - ar [ i - 1 ] == 1 ) count ++ ;
    else count = 1 ;
    if ( count == 3 ) {
      System . out . println ( "NO" ) ;
      System . exit ( 0 ) ;
    }
  }
  System . out . println ( "YES" ) ;
}

public static void main ( String arg [ ] ) { Scanner sc = new Scanner ( System . in ) ; long n = sc . nextInt ( ) ; int m = sc . nextInt ( ) ; int flag = 0 ; long [ ] ar = new long [ m ] ; for ( int i = 0 ; i < m ; i ++ ) { ar [ i ] = sc . nextLong ( ) ; if ( ar [ i ] == 1 || ar [ i ] == n ) flag = 1 ; } if ( flag == 1 ) { System . out . println ( " NO " ) ; System . exit ( 0 ) ; } Arrays . sort ( ar ) ; int count = 1 ; for ( int i = 1 ; i < m ; i ++ ) { if ( ar [ i ] - ar [ i - 1 ] == 1 ) count ++ ; else count = 1 ; if ( count == 3 ) { System . out . println ( " NO " ) ; System . exit ( 0 ) ; } } System . out . println ( " YES " ) ; }
(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) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (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)))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (decimal_integer_literal)) right: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (identifier)))) consequence: (expression_statement (assignment_expression left: (identifier) right: (decimal_integer_literal)))))) (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)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal)))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) (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 (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (decimal_integer_literal))) consequence: (expression_statement (update_expression (identifier))) alternative: (expression_statement (assignment_expression left: (identifier) right: (decimal_integer_literal)))) (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)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal)))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))