public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] num = new int [ n + 1 ] ;
  int ans = 0 ;
  int tmp ;
  num [ 0 ] = 10000000 ;
  for ( int i = 1 ;
  i <= n ;
  i ++ ) {
    num [ i ] = sc . nextInt ( ) ;
  }
  for ( int i = 1 ;
  i <= n ;
  i ++ ) {
    if ( i == n ) {
      if ( num [ i ] == i ) {
        tmp = num [ i ] ;
        num [ i ] = num [ i - 1 ] ;
        num [ i - 1 ] = tmp ;
        ans ++ ;
      }
    }
    else {
      if ( num [ i ] == i ) {
        tmp = num [ i ] ;
        num [ i ] = num [ i + 1 ] ;
        num [ i + 1 ] = tmp ;
        ans ++ ;
      }
    }
  }
  System . out . println ( ans ) ;
  sc . close ( ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] num = new int [ n + 1 ] ; int ans = 0 ; int tmp ; num [ 0 ] = 10000000 ; for ( int i = 1 ; i <= n ; i ++ ) { num [ i ] = sc . nextInt ( ) ; } for ( int i = 1 ; i <= n ; i ++ ) { if ( i == n ) { if ( num [ i ] == i ) { tmp = num [ i ] ; num [ i ] = num [ i - 1 ] ; num [ i - 1 ] = tmp ; ans ++ ; } } else { if ( num [ i ] == i ) { tmp = num [ i ] ; num [ i ] = num [ i + 1 ] ; num [ i + 1 ] = tmp ; ans ++ ; } } } System . out . println ( ans ) ; sc . close ( ) ; }
(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: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (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: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (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: (identifier) right: (identifier))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (identifier))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (array_access array: (identifier) index: (identifier)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (identifier))) (expression_statement (update_expression (identifier)))))) alternative: (block (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (identifier))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (array_access array: (identifier) index: (identifier)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (identifier))) (expression_statement (update_expression (identifier))))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))