var i,n,m:longint;
    ans,a,b,c,d,x,y:real;
begin
  ans:=0;
  readln(n,m);
  readln(a,b);c:=a;d:=b;
  for i:=2 to n do
   begin
    readln(x,y);
    ans:=ans+sqrt(sqr(x-a)+sqr(y-b));
    a:=x;b:=y;
   end;
  ans:=ans+sqrt(sqr(a-c)+sqr(b-d));
  ans:=ans+pi*2*m;
  writeln(ans:0:2);
end.