a[100],b[100000],C,N,i,k;

main(m){
	scanf("%d%d",&C,&N);
	for(;i<N;i++)scanf("%d",a+i);
	for(;m<=C;m++){
		k=-1;
		for(i=0;i<N;i++){
			if(m >= a[i] && b[m-a[i]] >= 0 && (k < 0 || b[m-a[i]] + 1 < k))
				k = b[m-a[i]] + 1;
		}
		b[m] = k;
	}
	printf("%d\n",b[C]?:-1);
	exit(0);
}