var

n,i,j,k:integer;

sum,r:real;

x,y:array[1..101] of real;

begin

read(n,r);

for i:=1 to n do

read(x[i],y[i]);

x[n+1]:=x[1];

y[n+1]:=y[1];

sum:=2*pi*r;

for i:=1 to n do

sum:=sum+sqrt(sqr(x[i]-x)+sqr(y[i]-y));

write(sum:0:2);

end.

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