#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] = {};
vector<int> max_ruizyou;
int main() {
	int m;
	cin >> m;
	vector<int> h;
	int a;
	h.push_back(0);
	while (cin >> a) {
		if (a == -1) break;
		h.push_back(a);
	}
	int hoge_hoge = 0;
	max_ruizyou.push_back(0);
	vector<int> min_ruizyou;
	long long wowowow = 0;
	for (int i = 0;i < h.size();++i) {
		wowowow += h[i]+1;
		if (i == 0) wowowow--;
		min_ruizyou.push_back(wowowow);
	}
	long long hogee = m;
	for (int i = 0;i < h.size();++i) {
		hogee -= h[i]+1;
	}
	hogee+=2;
	for (int i = 1;i < h.size();++i) {
		max_ruizyou.push_back(hogee);
		hogee += h[i]+1;
	}
	if (h[1] == 0) {
		cout << "1" << endl;
		return 0;
	}
	dp[0][0] = 1;
	for (int i = 1;i < h.size();++i) {
		long long now_tasu = 0;
		for (int q = min_ruizyou[i-1];q <= max_ruizyou[i];++q) {
			now_tasu += dp[q][(i+1)%2];
			now_tasu %= MAX_MOD;
			dp[q + h[i]+1][i % 2] += now_tasu;
			dp[q + h[i]+1][i % 2] %= MAX_MOD;
			dp[q][(i + 1) % 2] = 0;
		}
	}
	long long ans = 0;
	for (int i = min_ruizyou[h.size() - 1];i <= m+1;++i) {
		ans += dp[i][(h.size() - 1) % 2];
	}
	if (ans != 0) {
		cout << ans%MAX_MOD << endl;
	}
	else {
		cout << "NA" << endl;
	}
}