var n,i: integer;
x1,x2,y2,y1,xx,yy,e,r: real;
begin
 readln(n,r);
 readln(x1,y1);
 yy:=y1; xx:=x1;
 for i:=2 to n do
  begin
   readln(x2,y2);
   e:=e+sqrt(sqr(x2-x1)+sqr(y2-y1));
   x1:=x2; y1:=y2;
  end;
writeln((round((e+2*3.14159*r+sqrt(sqr(xx-x1)+sqr(yy-y1)))*100))/100);
end.