public static void main ( String [ ] args ) {
  Scanner scanner = new Scanner ( System . in ) ;
  int n = scanner . nextInt ( ) ;
  if ( n == 2 ) {
    System . out . println ( 1 ) ;
    return ;
  }
  int count = 0 ;
  for ( int i = 2 ;
  i < n ;
  i ++ ) {
    int power = 1 ;
    long root = i * i ;
    boolean check = true ;
    while ( power < n - 2 ) {
      if ( root % n == 1 ) {
        check = false ;
        break ;
      }
      root = ( root * i ) % n ;
      power ++ ;
    }
    if ( check ) count ++ ;
  }
  System . out . println ( count ) ;
}

public static void main ( String [ ] args ) { Scanner scanner = new Scanner ( System . in ) ; int n = scanner . nextInt ( ) ; if ( n == 2 ) { System . out . println ( 1 ) ; return ; } int count = 0 ; for ( int i = 2 ; i < n ; i ++ ) { int power = 1 ; long root = i * i ; boolean check = true ; while ( power < n - 2 ) { if ( root % n == 1 ) { check = false ; break ; } root = ( root * i ) % n ; power ++ ; } if ( check ) count ++ ; } System . out . println ( count ) ; }
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