# include <cstdio>
# include <cstring>
# include <cstdlib>
# include <iostream>
# include <vector>
# include <queue>
# include <stack>
# include <map>
# include <set>
# include <cmath>
# include <algorithm>
using namespace std;
# define lowbit(x) ((x)&(-x))
# define pi 3.1415926535
# define eps 1e-9
# define MOD 100000007
# define INF 1000000000
# define mem(a,b) memset(a,b,sizeof(a))
# define FOR(i,a,n) for(int i=a; i<=n; ++i)
# define FO(i,a,n) for(int i=a; i<n; ++i)
# define bug puts("H");
# define lch p<<1,l,mid
# define rch p<<1|1,mid+1,r
# define mp make_pair
# define pb push_back
typedef pair<int,int> PII;
typedef vector<int> VI;
# pragma comment(linker, "/STACK:1024000000,1024000000")
typedef long long LL;
int Scan() {int res=0, flag=0;char ch;if((ch=getchar())=='-') flag=1;else if(ch>='0'&&ch<='9') res=ch-'0';while((ch=getchar())>='0'&&ch<='9')  res=res*10+(ch-'0');return flag?-res:res;
}
void Out(int a) {if(a<0) {putchar('-'); a=-a;}if(a>=10) Out(a/10);putchar(a%10+'0');
}
const int N=10005;
//Code begin...int dee[155];
LL cc[155][155];void init()
{FOR(i,0,150) {cc[i][0]=1;FOR(j,1,i) cc[i][j]=cc[i-1][j-1]+cc[i-1][j];}
}
int main ()
{init();int n, sum=0;LL ans=1;scanf("%d",&n);if (n==1) {scanf("%d",dee);puts(dee[0]==0?"1":"0");return 0;}FOR(i,1,n) {scanf("%d",dee+i), --dee[i], sum+=dee[i];if (dee[i]<0) {puts("0"); return 0;}}if (sum!=n-2) {puts("0"); return 0;}FOR(i,1,n) {if (!dee[i]) continue;ans*=cc[sum][dee[i]];sum-=dee[i];}printf("%lld\n",ans);return 0;
}