var
begin
assign(input,'fact.in');reset(input);
assign(output,'fact.out');rewrite(output);
readln(p);
 if p<0 then write(-1)
        else if p=0 then write(1)
                    else
 begin
  for i:=1 to (p div 5) do begin
   if (i mod 4=1) and (i<>1) then
        inc(m);
   s:=s+10+m*5;
   nr:=nr+2+m; end;
end;
write(s+(p-nr)*5);
close(input);close(output);
end.