void Solve(ConsoleInput cin)
{
int n = cin.ReadInt;
long[] a_n = cin.ReadLongArray(n);
Console.WriteLine(a_n.Sum() - n);
}
public void Solve(ConsoleInput cin)
{
var N = cin.ReadInt;
var X = cin.ReadLong;
var m = cin.ReadLongArray(N);
var nokori = X - m.Sum();
var ans = nokori / m.Min() + m.Length;
WriteLine(ans);
}
void Solve(ConsoleInput cin)
{
int n = cin.ReadInt;
long[] a_n = cin.ReadLongArray(n);
Array.Sort(a_n);
Array.Reverse(a_n);
Dictionary <long, long> dict = new Dictionary <long, long>();
foreach (long a in a_n)
{
if (!dict.ContainsKey(a))
{
dict.Add(a, 0);
}
dict[a]++;
}
long ans = 0;
foreach (long a in a_n)
{
if (dict[a] == 0)
{
continue;
}
dict[a]--;
long powered = 1;
while (powered <= a)
{
powered <<= 1;
}
long b = powered - a;
if (dict.ContainsKey(b) && dict[b] > 0)
{
dict[b]--;
ans++;
}
}
Console.WriteLine(ans);
}