#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(void)
{
    int n, s;
    cin >> s >> n;
    
    vector<int> a(n);

    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    sort(a.begin(), a.end());

    int count = 0;
    for (int i = 0; i < n; i++) {
        if (binary_search(a.begin() + i + 1, a.end(), s - a[i])) {
            count++;
        }
    }

    cout << count << endl;

    return 0;
}