public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  PriorityQueue < Integer > pq = new PriorityQueue < > ( Collections . reverseOrder ( ) ) ;
  int n = sc . nextInt ( ) , x = sc . nextInt ( ) , c = 0 ;
  while ( n -- > 1 ) pq . add ( sc . nextInt ( ) ) ;
  while ( x <= pq . peek ( ) ) {
    pq . add ( pq . poll ( ) - 1 ) ;
    x ++ ;
    c ++ ;
  }
  System . out . println ( c ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; PriorityQueue < Integer > pq = new PriorityQueue < > ( Collections . reverseOrder ( ) ) ; int n = sc . nextInt ( ) , x = sc . nextInt ( ) , c = 0 ; while ( n -- > 1 ) pq . add ( sc . nextInt ( ) ) ; while ( x <= pq . peek ( ) ) { pq . add ( pq . poll ( ) - 1 ) ; x ++ ; c ++ ; } System . out . println ( c ) ; }
(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: (generic_type (type_identifier) (type_arguments (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments)) arguments: (argument_list (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))) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (while_statement condition: (parenthesized_expression (binary_expression left: (update_expression (identifier)) right: (decimal_integer_literal))) body: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (while_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) body: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (decimal_integer_literal))))) (expression_statement (update_expression (identifier))) (expression_statement (update_expression (identifier))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))