static void solve ( ) {
  int n = ni ( ) ;
  List < Integer > arr = new ArrayList < > ( ) ;
  for ( int i = 0 ;
  i < n ;
  ++ i ) {
    arr . add ( ni ( ) ) ;
  }
  Collections . sort ( arr ) ;
  if ( n % 2 != 0 ) {
    int k = 0 ;
    long sum = 0 ;
    for ( int i = 0 ;
    i < n ;
    i = i + 2 ) {
      sum = sum + arr . get ( i ) * arr . get ( i ) - k * k ;
      if ( i != n - 1 ) {
        k = arr . get ( i + 1 ) ;
      }
    }
    double ans = Math . PI * ( double ) sum ;
    out ( ans ) ;
  }
  else {
    int k = arr . get ( 0 ) ;
    long sum = 0 ;
    for ( int i = 1 ;
    i < n ;
    i = i + 2 ) {
      sum = sum + arr . get ( i ) * arr . get ( i ) - k * k ;
      if ( i != n - 1 ) {
        k = arr . get ( i + 1 ) ;
      }
    }
    double ans = Math . PI * ( double ) sum ;
    out ( ans ) ;
  }
}

static void solve ( ) { int n = ni ( ) ; List < Integer > arr = new ArrayList < > ( ) ; for ( int i = 0 ; i < n ; ++ i ) { arr . add ( ni ( ) ) ; } Collections . sort ( arr ) ; if ( n % 2 != 0 ) { int k = 0 ; long sum = 0 ; for ( int i = 0 ; i < n ; i = i + 2 ) { sum = sum + arr . get ( i ) * arr . get ( i ) - k * k ; if ( i != n - 1 ) { k = arr . get ( i + 1 ) ; } } double ans = Math . PI * ( double ) sum ; out ( ans ) ; } else { int k = arr . get ( 0 ) ; long sum = 0 ; for ( int i = 1 ; i < n ; i = i + 2 ) { sum = sum + arr . get ( i ) * arr . get ( i ) - k * k ; if ( i != n - 1 ) { k = arr . get ( i + 1 ) ; } } double ans = Math . PI * ( double ) sum ; out ( ans ) ; } }
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