public static void main ( String args [ ] ) throws Exception {
  Scanner sc = new Scanner ( System . in ) ;
  int N = sc . nextInt ( ) ;
  int [ ] p = new int [ N ] ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    p [ i ] = sc . nextInt ( ) - 1 ;
  }
  int pos = 0 ;
  int ans = 0 ;
  while ( pos < N ) {
    if ( pos == p [ pos ] ) {
      if ( pos != N - 1 ) {
        if ( pos + 1 == p [ pos + 1 ] ) {
          ans ++ ;
          pos += 2 ;
        }
        else {
          ans ++ ;
          pos ++ ;
        }
      }
      else {
        ans ++ ;
        pos ++ ;
      }
    }
    else {
      pos ++ ;
    }
  }
  System . out . println ( ans ) ;
}

public static void main ( String args [ ] ) throws Exception { Scanner sc = new Scanner ( System . in ) ; int N = sc . nextInt ( ) ; int [ ] p = new int [ N ] ; for ( int i = 0 ; i < N ; i ++ ) { p [ i ] = sc . nextInt ( ) - 1 ; } int pos = 0 ; int ans = 0 ; while ( pos < N ) { if ( pos == p [ pos ] ) { if ( pos != N - 1 ) { if ( pos + 1 == p [ pos + 1 ] ) { ans ++ ; pos += 2 ; } else { ans ++ ; pos ++ ; } } else { ans ++ ; pos ++ ; } } else { pos ++ ; } } System . out . println ( ans ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier) dimensions: (dimensions))) (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 (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 (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: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) 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) value: (decimal_integer_literal))) (while_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier)))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) consequence: (block (expression_statement (update_expression (identifier))) (expression_statement (assignment_expression left: (identifier) right: (decimal_integer_literal)))) alternative: (block (expression_statement (update_expression (identifier))) (expression_statement (update_expression (identifier)))))) alternative: (block (expression_statement (update_expression (identifier))) (expression_statement (update_expression (identifier)))))) alternative: (block (expression_statement (update_expression (identifier))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))