#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <iomanip>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(int i = 0;i < n;++i)
long long dp[1000100][2] = {};
int main() {
	int m;
	cin >> m;
	int a = 1;
	vector<int> hints;
	while (cin >> a){
		hints.push_back(a);
	}
	if (hints[0] == 0) {
		cout << "1" << endl;
		return 0;
	}
	dp[0][1] = 1;
	for (int i = 0;i < hints.size();++i) {
		for (int q = 0;q < m;++q) {
			if (q + hints[i] <= m) {
				dp[q + hints[i] + 1][i % 2] += dp[q][(i + 1) % 2];
			}
			dp[q + hints[i] + 1][i % 2] %= MAX_MOD;
			dp[q + 1][(i + 1) % 2] += dp[q][(i + 1) % 2];
			dp[q][(i + 1) % 2] = 0;
		}
	}
	long long ans = 0;
	for (int i = 0;i <= m;++i) {
		ans += dp[i][hints.size() % 2];
		ans %= MAX_MOD;
	}
	if (ans != 0) {
		cout << ans%MAX_MOD << endl;
	}
	else {
		cout << "NA" << endl;
	}
}