P=1e9+7;long v[1<<20];s,n,k,i,t;main(j){for(v[1]=s=scanf("%d",&n);j++<n?v[j]=v[P%j]*(P-P/j)%P:~scanf("%d",&t)?n-=t,k+=!!t:k/++i?s=s*v[i]%P*(n-i+2)%P:0;);printf(s?"%d":"NA",s);}