#include <iostream>
#include <vector>
using namespace std;

int main() {
  int n,q;
  vector<int> S,T;

  cin >> n;
  for(int i=0;i<n;i++) {
    int s;
    cin >> s;
    S.push_back(s);
  }
  cin >> q;
  for(int i=0;i<q;i++) {
    int t;
    cin >> t;
    T.push_back(t);
  }

  // O(n^2)
  int C = 0;
  for(int t_itr=0;t_itr<q;t_itr++) {
    int key = T[t_itr];
    for(int s_itr=0;s_itr<n;s_itr++) {
      if(S[s_itr] == key) {
        C++;
        break;
      }
    }
  }

  cout << C << endl;
}
#pragma region
#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <set>
#include <list>
#include <iomanip>
#include <cstdint>
#include <bitset>

using namespace std;
typedef long long ll;
//#define rep(i, s, e) for (int(i) = (s); (i) < (e); ++(i))
#define rep(i, e) for (int(i) = 0; (i) < (e); ++(i))
#define rrep(i, s) for (int(i) = (s) - 1; (i) >= 0; --(i))
#define all(x) x.begin(),x.end()

#pragma region UnionFind
struct UnionFind
{
	vector<int> par;

	UnionFind(int n) : par(n, -1) {}
	void init(int n) { par.assign(n, -1); }

	int root(int x)
	{
		if (par[x] < 0) return x;
		else return par[x] = root(par[x]);
	}

	bool issame(int x, int y)
	{
		return root(x) == root(y);
	}

	bool merge(int x, int y)
	{
		x = root(x); y = root(y);
		if (x == y) return false;
		if (par[x] > par[y]) swap(x, y);
		par[x] += par[y];
		par[y] = x;
		return true;
	}

	int size(int x)
	{
		return -par[root(x)];
	}
};
#pragma endregion
#pragma region GCD
int gcd(int a, int b)
{
	if (a%b == 0)return b;
	return gcd(b, a%b);
}
#pragma endregion
#pragma region chmin
template<class T> inline bool chmin(T& a, T b)
{
	if (a > b)
	{
		a = b;
		return true;
	}
	return false;
}
#pragma endregion
#pragma region chmax
template<class T> inline bool chmax(T& a, T b)
{
	if (a < b)
	{
		a = b;
		return true;
	}
	return false;
}
#pragma endregion
#pragma endregion


int main()
{
	int n; cin >> n;
	vector<ll> a(n);
	map<ll, int> mp;
	rep(i, n)
	{
		cin >> a[i];
		++mp[a[i]];
	}
	sort(all(a), greater<ll>());
	int res = 0;
	rep(i, n)
	{
		if (!mp[a[i]])continue;
		--mp[a[i]];
		ll tmp = 1;
		while (tmp <= a[i])tmp = tmp << 1;
		if (mp[tmp - a[i]])
		{
			--mp[tmp - a[i]];
			++res;
		}
	}
	cout << res << endl;
}