public static void main ( String [ ] args ) throws IOException {
  BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ;
  String [ ] str = br . readLine ( ) . split ( " " ) ;
  int n = Integer . parseInt ( str [ 0 ] ) ;
  int m = Integer . parseInt ( str [ 1 ] ) ;
  long base = ( long ) 1e9 + 7 ;
  long ans = 1 ;
  if ( Math . abs ( n - m ) == 0 ) {
    ans *= 2 ;
    ans %= base ;
  }
  else if ( Math . abs ( n - m ) > 1 ) {
    System . out . println ( 0 ) ;
    System . exit ( 0 ) ;
  }
  for ( int i = 1 ;
  i <= n ;
  i ++ ) {
    ans *= i ;
    ans %= base ;
  }
  for ( int i = 1 ;
  i <= m ;
  i ++ ) {
    ans *= i ;
    ans %= base ;
  }
  System . out . println ( ans ) ;
}

public static void main ( String [ ] args ) throws IOException { BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ; String [ ] str = br . readLine ( ) . split ( " ▁ " ) ; int n = Integer . parseInt ( str [ 0 ] ) ; int m = Integer . parseInt ( str [ 1 ] ) ; long base = ( long ) 1e9 + 7 ; long ans = 1 ; if ( Math . abs ( n - m ) == 0 ) { ans *= 2 ; ans %= base ; } else if ( Math . abs ( n - m ) > 1 ) { System . out . println ( 0 ) ; System . exit ( 0 ) ; } for ( int i = 1 ; i <= n ; i ++ ) { ans *= i ; ans %= base ; } for ( int i = 1 ; i <= m ; i ++ ) { ans *= i ; ans %= base ; } System . out . println ( ans ) ; }
(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: (binary_expression left: (cast_expression type: (integral_type) value: (decimal_floating_point_literal)) right: (decimal_integer_literal)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (identifier)))) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (decimal_integer_literal))) (expression_statement (assignment_expression left: (identifier) right: (identifier)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (identifier)))) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (decimal_integer_literal)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (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: (identifier) right: (identifier))) (expression_statement (assignment_expression left: (identifier) right: (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: (identifier) right: (identifier))) (expression_statement (assignment_expression left: (identifier) right: (identifier))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))