#include<stdio.h>
#include<string.h>

int coins[100];
int n;
int impossible = 10000;
int dp[1000];

int decompose(int s) {
    if (dp[s] != -1)
        return dp[s];

    if (s == 0)
        return 0;

    int best = impossible;
    if (s < coins[n-1]) {
        dp[s] = impossible;
        return impossible;
    }

    for (int i = 0; i < n; i++) {
        if (s >= coins[i]) {
            int res = decompose(s - coins[i]) + 1;
            if (res < best)
                best = res;
        }
    }
    dp[s] = best;
    return best;
}

int main() {
    int s;
    memset(dp, -1, sizeof(dp));
    scanf("%d %d", &s, &n);
    for (int i = 0; i < n; i++)
        scanf("%d", &coins[i]);

    int result = decompose(s);
    printf("%d", (result == impossible)?-1:result);
    return 0;
}