var p,n,i,a,b,c,m:longint;
    f,g:text;
begin
assign(f,'fact.in');reset(f);
assign(g,'fact.out');rewrite(g);
read(f,p);
if p=0 then
writeln(g,1)
else begin
a:=0;
b:=maxlongint;
while (a<=b)and(c<>p) do
begin
m:=a+b;
c:=m div 2;
if c=p then
write(g,c)
else if c<p then
a:=c+1
else b:=c-1;
end;
if c<>p then
writeln(g,-1);
end;
close(g);
end.