#include<bits/stdc++.h> using namespace std; long long a[100005]; long long fac[25]; int n; int t; int sum =0; int main(){ cin>>n; fac[0]=1; for(int i = 1;i<=20;i++){ fac[i]=fac[i-1]*i; } for(int i = 1;i<=n;i++){ cin>>a[i]; sum+=a[i]; } long long ans =1; for(int i = 1;i<=n;i++){ if(a[i]!=1) ans*=(fac[sum-1]/fac[sum-1-(a[i]-1)]/fac[a[i]-1]); sum-=a[i]; } cout<<ans<<endl; }