a,b[100001],C,N,i;main(m){
	scanf("%d%d",&C,&N);
	*b=1;
	for(i=0;i<N;i++)for(scanf("%d",&a),m=a;m<=C;m++)if(b[m-a]&&(!b[m]||b[m-a]<b[m]))b[m]=b[m-a]+1;
	C=!printf("%d\n",b[C]-1);
}