const eps = 0;
type real = extended;
type tpoint = record x, y: real; end;
var n, l: longint;
mas: array [1..1000] of tpoint;
an: array [1..1000] of real;
ob: array [1..1000] of boolean;
ans: array [1..1000] of longint;
a, ang: real;
i, j, k: longint;
c, t: tpoint;
v: array [1..3] of longint;
function getan(p: tpoint): real;
var x: real;
begin
if p.x=0 then
begin
if p.y>0 then getan:=pi/2 else getan:=-pi/2;
exit;
end;
x:=p.y/p.x;
getan:=arctan(x);
end;
procedure fconvex;
var vp: real;
v1, v2: tpoint;
begin
v[1]:=2;
v[2]:=3;
v[3]:=4;
i:=4;
repeat
v1.x:=mas[v[2]].x-mas[v[1]].x; v1.y:=mas[v[2]].y-mas[v
[1]].y;
v2.x:=mas[v[3]].x-mas[v[2]].x; v2.y:=mas[v[3]].y-mas[v
[2]].y;
vp:=v1.x*v2.y-v1.y*v2.x;
if vp<eps then
begin
ob[v[2]]:=false;
dec(k);
v[2]:=v[1];
dec(v[1]);
while ob[v[1]]= false do dec(v[1]);
end else
begin
v[1]:=v[2]; v[2]:=v[3]; i:=i mod n + 1; v[3]:=i;
end;
until i=2;
end;
begin
read(n, l);
c.x:=maxlongint;
c.y:=maxlongint;
fillchar(ob, sizeof(ob), false);
for i:=1 to n do
begin
read(mas[i].x, mas[i].y);
if (mas[i].x<c.x)or((mas[i].y<c.y)and(mas[i].x=c.x)) then
c:=mas[i];
end;
for i:=1 to n do
begin
t.x:=mas[i].x-c.x;t.y:=mas[i].y-c.y;
an[i]:=getan(t);
j:=i;
while (j>1)and(an[j]<an[j-1]) do
begin
a:=an[j];
an[j]:=an[j-1];
an[j-1]:=a;
t:=mas[j];
mas[j]:=mas[j-1];
mas[j-1]:=t;
dec(j);
end;
end;
fillchar(ob, sizeof(ob), true);
k:=n;
if n>3 then
fconvex;
i:=1;
j:=0;
repeat
while (i<n)and(not ob[i]) do inc(i);
inc(j);
ans[j]:=i;
inc(i);
until j=k;
a:=0;
for i:=1 to k-1 do
begin
ang:=sqr(mas[ans[i]].x-mas[ans[i+1]].x)+sqr(mas[ans[i]].y-
mas[ans[i+1]].y);
ang:=sqrt(ang);
a:=a+ang;
end;
ang:=sqrt(sqr(mas[ans[k]].x-mas[ans[1]].x)+sqr(mas[ans[k]].y-mas
[ans[1]].y));
a:=a+ang;
a:=a+2*pi*l;
writeln(a:0:0);
end.
Why my solution works if eps=0 and doesn't work if eps is for example
0.00000000001
