program rope;
 var n,i:integer;
     r:extended;
     a:array[1..100] of record x,y:extended;  end;
     res:extended;
begin
  read(n); read(r); res:=0;
  for i:=1 to n do Readln(a[i].x,a[i].y);
  for i:=2 to n do res:=res+sqrt(sqr(a[i].x-a[i-1].x)+sqr(a[i].y-a[i-
1].y));
  res:=res+sqrt(sqr(a[n].x-a[1].x)+sqr(a[n].y-a[1].y));
  res:=res+2*pi*r;
  writeln(res:0:2);
end.