var

n,r,i:integer;

a,b,c,d,l,x,y:real;

begin

read(n,r);

c:=0;d:=0;

readln(x,y);

for i:=2 to n do

begin

readln(a,b);

l:=sqrt(sqr(a-c)+sqr(b-d))+l;

c:=a;d:=b;

end;

l:=l+sqrt(sqr(a-x)+sqr(b-y))+2*r*3.1415926;

write(l:0:2);

end.