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var n,i:longint;
    r,x0,y0,x,y,x1,y1,s:real;
begin
  readln(n,r);
  readln(x0,y0);
  x:=x0;
  y:=y0;
  for i:=2 to n do begin
    readln(x1,y1);
    s:=s+sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
    x:=x1;
    y:=y1;
  end;
  s:=s+sqrt((x0-x)*(x0-x)+(y0-y)*(y0-y))+2*pi*r;
  writeln(s:0:2);
end.