#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,n,0)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 100000000

typedef long long ll;

int a[100001];
int dp[100001];

int main() {
    int i, j, c, n;
    cin >> c >> n;
    fill(dp+1,dp+c+1,INF);
    rep (i,n) {
        int a;
        cin >> a;
        REP (j,a,c+1) dp[j] = min(dp[j-a]+1,dp[j]);
    }
    if (dp[c] != INF)
        cout << dp[c] << endl;
    else
        cout << -1 << endl;
    return 0;
}