#include <bits/stdc++.h>
using namespace std;
map<int, int> m;
bool fd(int x, int y) {
  if (x == y) return m[y] >= 2;
  return m.find(y) != m.end();
}
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < (n); i++) {
    int x;
    cin >> x;
    m[x]++;
  }
  int cnt = 0;
  for (auto& xp : m) {
    int x = xp.first;
    for (int s = 1; s <= 30; s++) {
      if ((1 << s) <= x) continue;
      if (fd(x, (1 << s) - x)) goto cont;
    }
    cnt += xp.second;
  cont:;
  }
  cout << cnt << endl;
  return 0;
}
