#include <iostream>
using namespace std;
#define INF 1000000
#define REP(i,j) for(int i = 0; i < j; i++)
int main(void){
    int c,n;
    int a[100];
    int dp[100001];
    cin >> c;
    cin >> n;
    REP(i,n) cin >> a[i];
    REP(i,c+1) dp[i] = INF;
    dp[0] = 0;
    REP(i,c + 1){ 
        REP(j,n) {
            if( i + a[j] <= c){
                dp[i + a[j]] = min(dp[i] + 1, dp[i + a[j]]);
            }
        }
    }
    if (dp[c] > c){
        dp[c] = -1;
    }
    cout << dp[c] << endl;
}