program Project1;
var i,n:integer;p:real;x,y:array [1..100] of real;f:text;
function L(x1,y1,x2,y2:real):real;
begin
L:=sqrt(sqr(x2-x1)+sqr(y2-y1));
end;
begin
assign(f,'input.dat');reset(f);
readln(f,n);
for i:=1 to n do
readln(f,x[i],y[i]);
x[n+1]:=x[1];y[n+1]:=y[1];close(f);
assign(f,'output.sol');rewrite(f);
for i:=1 to n do p:=p+L(x[i],y[i],x[i+1],y[i+1]);
write(f,p:0:2);close(f);
end.