public static void main ( String args [ ] ) {
  Scanner sc = new Scanner ( System . in ) ;
  long n = sc . nextLong ( ) ;
  long k = sc . nextLong ( ) ;
  long half = k / 2 ;
  if ( n < half ) {
    System . out . println ( "0" ) ;
  }
  else System . out . println ( ( Math . min ( n , k - 1 ) ) - half ) ;
}

public static void main ( String args [ ] ) { Scanner sc = new Scanner ( System . in ) ; long n = sc . nextLong ( ) ; long k = sc . nextLong ( ) ; long half = k / 2 ; if ( n < half ) { System . out . println ( "0" ) ; } else System . out . println ( ( Math . min ( n , k - 1 ) ) - half ) ; }
(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: (binary_expression left: (identifier) right: (decimal_integer_literal)))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) consequence: (block (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 (binary_expression left: (parenthesized_expression (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (binary_expression left: (identifier) right: (decimal_integer_literal))))) right: (identifier))))))))