#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int n;
ll T;
vector<ll> a;

bool dfs_pack(int idx, vector<ll>& bins) {
    if (idx == n) return true;
    ll cur = a[idx];
    int k = bins.size();
    for (int j = 0; j < k; ++j) {
        if (bins[j] + cur <= T) {
            bool skip = false;
            for (int s = 0; s < j; ++s) if (bins[s] == bins[j]) { skip = true; break; }
            if (skip) continue;
            bins[j] += cur;
            if (dfs_pack(idx + 1, bins)) return true;
            bins[j] -= cur;
            if (bins[j] == 0) break;
        }
    }
    return false;
}

bool can_pack_with_k(int k) {
    ll sum = 0;
    for (ll v : a) sum += v;
    if (sum > (ll)k * T) return false;
    vector<ll> bins(k, 0);
    return dfs_pack(0, bins);
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> T;
    cin >> n;
    a.resize(n);
    for (int i = 0; i < n; ++i) cin >> a[i];
    ll mx = *max_element(a.begin(), a.end());
    if (mx > T) {
        cout << -1 << '\n';
        return 0;
    }
    ll sum = 0;
    for (ll v : a) sum += v;
    int low = max(1LL, (sum + T - 1) / T);
    int high = n;
    sort(a.rbegin(), a.rend());
    int ans = high;
    while (low <= high) {
        int mid = (low + high) / 2;
        if (can_pack_with_k(mid)) {
            ans = mid;
            high = mid - 1;
        } else low = mid + 1;
    }
    cout << ans << '\n';
}