#include <iostream>
#include <algorithm>
using namespace std;
int v[100001];
int main()
{
    int n,j,i,ok = 1,cnt=0,mid,st,dr;
    cin >> n;
    for(i=0; i<n; i++)
        cin >> v[i];

    sort(v,v+n);

    for(i=0 ; i<n; i++)
    {
        for(int s = 1; s <= 1000000000; s = s * 2)
        {
            ok = 1;
            j = s - v[i];
            st = i+1, dr = n-1;
            while(st <= dr)
            {
                mid = (st + dr) / 2;
                if(v[mid] < j)
                    st = mid + 1;
                else if(v[mid] > j)
                    dr = mid - 1;
                else
                {
                    ok = 0;
                    break;
                }
            }
            if(ok == 0)
                cnt++;
        }
    }
    cout << cnt;
    return 0;
}