#include <iostream>
#include <vector>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
#define repeat_from(i,m,n) for (int i = (m); (i) < (n); ++(i))
template <class T> bool setmin(T & l, T const & r) { if (not (r < l)) return false; l = r; return true; }
using namespace std;
const int inf = 1e9+7;
int main() {
    int c, n; cin >> c >> n;
    vector<int> as(n); repeat (i,n) cin >> as[i];
    vector<int> dp(c+1, inf);
    dp[0] = 0;
    repeat_from (i,1,c+1) {
        for (int a : as) {
            if (0 <= i-a) {
                setmin(dp[i], dp[i-a] + 1);
            }
        }
    }
    cout << (dp[c] == inf ? -1 : dp[c]) << endl;
    return 0;
}