var p,i,m,nr,s:int64;
begin
assign(input,'fact.in');reset(input);
assign(output,'fact.out');rewrite(output);
readln(p);
m:=0; s:=0;
 if p<0 then write(-1)
        else if p=0 then write(1)
                    else
 begin
  for i:=1 to (p div 5) do
   if (i mod 4=1) and (i<>1) then inc(m);
s:=s*p - m*5;
end;
write(s);
close(input);close(output);
end.