import java.util.Scanner;
public class _1020
{
    public static void main( String[] args )
    {
        Scanner in = new Scanner( System.in );
        int N = in.nextInt();
        double R = in.nextDouble();
        double[][] p = new double[N][2];
        double PI = Math.PI;
        double L = 2*PI*R;
        for( int i=0 ; i<N ; i++ )
        {
            p[i][0] = in.nextDouble();
            p[i][1] = in.nextDouble();
            if( i>0 )    L += Math.sqrt( (p[i][1]-p[i-1][1])*(p[i][1]-p[i-1][1]) + (p[i][0]-p[i-1][0])*(p[i][0]-p[i-1][0]) );
        }
        L += Math.sqrt( (p[0][1]-p[N-1][1])*(p[0][1]-p[N-1][1]) + (p[0][0]-p[N-1][0])*(p[0][0]-p[N-1][0]) );
        System.out.println( String.format("%.2f", L) );
    }
}