program Project2;

{$APPTYPE CONSOLE}
var
x,y:array[1..100]of real;
i,n,m:integer;
l,p,x1,x2,y1,y2:real;
 f1,f2:text;
begin
assign(f1,'vx.txt');
readl(f1,n);
rewriite(f2,'vxu.txt');
readln(n);

 for i:=1 to n do
 read(x[i],y[i]);
 x[n+1]:=x[1] ;
 y[n+1]:=y[1] ;
    for i:=1 to n do
p:=p+sqrt(sqr(x[i+1]-x[i])+sqr(y[i+1]-y[i]));
 writeln(f2,P:5:2);
  close(f1);
  close(f2);
 readln;
   readln;
end.