uses crt;
type kor=record
     x,y:integer;
end;
var i,n:integer;
p:real;
       r,m:array[1..100] of kor;
       f:text;
       k,l,k1,k2,l1,l2:integer;

function fl(x1,y1,x2,y2:integer):boolean;
var xx,yy:real;
begin
fl:=true;
if x1<>x2 then
for i:=k1 to k2 do
if m[i].y>(m[i].x-x1)*(y2-y1)/(x2-x1)+y1 then fl:=false;
{(y-y1)/(y2-y1)=(x-x1)/(x2-x1)
y=(x-x1)*(y2-y1)/(x2-x1)+y1
}
end;

function fr(x1,y1,x2,y2:integer):boolean;
var xx,yy:real;
begin
fr:=true;
if x1<>x2 then
for i:=l1 to l2 do
if m[i].y<(m[i].x-x1)*(y2-y1)/(x2-x1)+y1 then fr:=false;
end;
procedure sort;
var temp,nm,max,k:integer;
begin
k:=n;
while k>1 do begin
max:=m[1].x;nm:=1;
for i:=2 to k do
if m[i].x>max then begin nm:=i; max:=m[i].x;end;
temp:=m[nm].x;m[nm].x:=m[k].x;m[k].x:=temp;
temp:=m[nm].y;m[nm].y:=m[k].y;m[k].y:=temp;

k:=k-1;
end;

end;

procedure out1;
begin
for i:=l to k do
with r[i] do begin writeln(x,' ',y);end;

end;

begin
clrscr;
assign(f,'int.txt');
reset(f);
readln(f,n);
for i:=1 to n do
            with m[i] do readln(f,x,y);
close(f);

sort;

k1:=1;k2:=n;
k:=n;
l1:=1;l2:=n;
l:=n;

r[k].x:=m[k1].x;r[k].y:=m[k1].y;

while (k1<>k2) do begin
if fl(m[k1].x,m[k1].y,m[k2].x,m[k2].y) then begin
                                            k:=k+1;
                                            r[k].x:=m[k2].x;
                                            r[k].y:=m[k2].y;
                                            k1:=k2;k2:=n;
                                            end
                                            else begin
                                            k2:=k2-1;
                                            end;
end;

while (l1<>l2) do begin
if fr(m[l1].x,m[l1].y,m[l2].x,m[l2].y) then begin
                                            l:=l-1;
                                            r[l].x:=m[l2].x;
                                            r[l].y:=m[l2].y;
                                            l1:=l2;l2:=n;
                                            end
                                            else begin
                                            l2:=l2-1;
                                            end;
end;
P:=0;
FOR i:=l to k-1 do p:=p+sqrt(sqr(r[i+1].x-r[i].x)+sqr(r[i+1].y-r[i].y));

out1;
writeln('P=',p:5:3);


end.