#include <iostream>
#include <vector>

constexpr int INF = 1 << 30;

void solve() {
    int c, n;
    std::cin >> c >> n;

    std::vector<int> dp(c + 1, INF);
    dp[0] = 0;
    while (n--) {
        int a;
        std::cin >> a;
        for (int x = a; x <= c; ++x) {
            dp[x] = std::min(dp[x], dp[x - a] + 1);
        }
    }

    auto ans = dp[c];
    std::cout << (ans == INF ? -1 : ans) << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}