program Project7;

{$APPTYPE CONSOLE}
var x,y:array[1..100] of real;
i,n:integer;
p:real;
function l(x1,y1,x2,y2:real):real;
begin


l:=sqrt(sqr(x2-x1)+sqr(y2-y1));
end;
begin
assign(input,'input.txt');
reset(input);
assign(output,'output.txt');
rewrite(output);
readln(n);
for i:=1 to n do readln(x[i],y[i]);
x[n+1]:=x[1];
y[n+1]:=y[1];
p:=0;
for i:=1 to n do p:=p+l(x[i],y[i],x[i+1],y[i+1]);
writeln(p);
close(input);
close(output);
end.