program p1007;

var s,a,b,x,y,x1,y1,r:real;

n,i:integer;

begin

read(n,r);

read(x1,y1);

s:=0;

x:=x1;y:=y1;

for i:=2 to n do

begin

readln(a,b);

s:=s+sqrt(sqr(a-x)+sqr(b-y));

x:=a;

y:=b;

end;

s:=s+sqrt(sqr(a-x1)+sqr(b-y1));

s:=s+2*r*3.1415926;

write(s:0:2);

end.