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

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