#include "bits/stdc++.h"
using namespace std;

#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()

int N,C;
int dp[511111];
signed main()
{
    cin>>C>>N;
    vector<int> A(N);
    REP(i,N) cin >> A[i];
    sort(ALL(A));
    REP(j,C+1) dp[j] = 1e9;
    dp[0] = 0;
    REP(i,N) REP(j,C+1) {
        int a = A[i];
        dp[j+a] = min(dp[j+a], 1 + dp[j]);
    }
    cout << (dp[C] < 1e9 ? dp[C] : -1) << endl;
    return 0;
}