x[200010],c,i;main(j){for(*x=scanf("%d%*d",&c);~scanf("%d",&j);)for(i=0;i<c;i++)x[i]&&!x[i+j]|x[i+j]>x[i]?x[i+j]=x[i]+1:0;i=!printf("%d",x[c]-1);}