#include<bits/stdc++.h> using namespace std; typedef long long ll; ll a[25]; ll c(ll x,ll y){ ll s1=1,s2=1; for(ll i=x;i>=x-y+1;i--){ s1*=i; } for(ll i=y;i>=1;i--){ s2*=i; } return s1/s2; } int main(){ ll n,sum=0; scanf("%lld",&n); for(ll i=1;i<=n;i++){ cin>>a[i]; sum+=a[i]; } ll ans=1; for(ll i=1;i<=n;i++){ ans*=c(sum-1,a[i]-1); sum-=a[i]; } cout<<ans<<endl; return 0; }