#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
// constexpr int mod = 1000000007;
constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

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

    int C, N;
    cin >> C >> N;
    vector<int> a(N);
    for(int i = 0; i < N; ++i)  cin >> a[i];

    vector<vector<int>> dp(N + 1, vector<int>(C + 1, INF));
    dp[0][0] = 0;
    int counter = 0;
    for(int i = 0; i < N; ++i){
        for(int m = 0; m < a[i]; ++m){
            int minv = INF;
            for(int s = m; s <= C; s += a[i]){
                minv += 1;
                chmin(minv, dp[i][s]);
                chmin(dp[i + 1][s], minv);
            }
        }
    }

    int ans = dp[N][C];
    if(ans == INF)  ans = -1;
    cout << ans << endl;

    return 0;
}