public static void main ( String [ ] args ) throws IOException {
  FastReader in = new FastReader ( ) ;
  PrintWriter pw = new PrintWriter ( System . out ) ;
  long m = in . nextLong ( ) ;
  long R = in . nextLong ( ) ;
  pw . printf ( "%.12f\n" , ( 2 + 2. * ( m - 1 ) * m * ( m + 1 ) / 3 / m / m - 2 * ( 2 - Math . sqrt ( 2 ) ) + ( 2 - Math . sqrt ( 2 ) ) * ( 2 * m + 2 * ( m - 1 ) ) / m / m ) * R ) ;
  pw . flush ( ) ;
  pw . close ( ) ;
}

public static void main ( String [ ] args ) throws IOException { FastReader in = new FastReader ( ) ; PrintWriter pw = new PrintWriter ( System . out ) ; long m = in . nextLong ( ) ; long R = in . nextLong ( ) ; pw . printf ( " % .12f \n " , ( 2 + 2. * ( m - 1 ) * m * ( m + 1 ) / 3 / m / m - 2 * ( 2 - Math . sqrt ( 2 ) ) + ( 2 - Math . sqrt ( 2 ) ) * ( 2 * m + 2 * ( m - 1 ) ) / m / m ) * R ) ; pw . flush ( ) ; pw . close ( ) ; }
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