#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cstring>
#include <complex>
#include <stack>
#include <queue>
#include <unordered_map>
#include <map>


using namespace std ;

#define MAX 1000001
#define MOD 1000000007
pair<pair<vector<long long int>, vector<long long int>>, vector<long long int>> COMinit()
{
    vector<long long int> fac;
    fac.push_back(1);
    fac.push_back(1);
    vector<long long int> finv;
    finv.push_back(1);
    finv.push_back(1);
    vector<long long int> inv;
    inv.push_back(1);
    inv.push_back(1);
    for (int i = 2; i < MAX+1; i++)
    {
        fac.push_back(fac[i - 1] * i % MOD);
        inv.push_back(MOD - ((inv[MOD % i] * (MOD / i)) % MOD));
        finv.push_back(finv[i - 1] * inv[i] % MOD);
        
    }
    return make_pair(make_pair(fac, finv), inv);
}

long long int COM(long long int n, long long int k, pair<pair<vector<long long int>, vector<long long int>>, vector<long long int>> &x)
{   
    return x.first.first[n] * x.first.second[k] % MOD * x.first.second[n - k] % MOD;
}
int main(){
    
   
    long long int M;
    cin >> M;
    vector<long long int> k;
    long long int s = 0;
    for(int i = 0; i < M; i++){
        int a;
        cin >> a;
        if(a == 0){
            cout << 1 << endl;
            return 0;
        }
        if(cin.eof()) break;
        k.push_back(a);
        s += a;
    }
    if(M-s < k.size()-1){
        cout << "NA" << endl;
        return 0;
    }
    long long int ans = 0;
    pair<pair<vector<long long int>, vector<long long int>>, vector<long long int>> x = COMinit();
    ans = COM((k.size()+1)+(M-s-(k.size()-1)-1),(M-s-(k.size()-1)),x);
    cout << ans << endl;
    return 0;
}