#include <iostream>
#include <set>

using namespace std;

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

    set<int> nums;

    int count = 0;
    while (n--) {
        int x;
        cin >> x;
        auto it = nums.find(s - x);
        if (it != nums.end()) {
            count++;
        }
        nums.insert(x);
    }

    cout << count << endl;
    
    return 0;
}