#include<stdio.h>

int C[3001][501];

int solve(int m, int n)
{
	if(m < 0 || m < n) return 0;
	for(int i = 0; i <= m; ++i)
	{
		for(int j = 0; j <= i && j <= n; ++j)
		{
			if(j == 0 || j == i) C[i][j] = 1;
			else C[i][j] = (C[i-1][j-1] + C[i-1][j]) % 1000000007;
		}
	}
	return C[m][n];
}

int main()
{
	int w, n, sum = 0;
	scanf("%d%d", &w, &n);
	for(int i = 0; i < n; ++i)
	{
		int tmp;
		scanf("%d", &tmp);
		sum += tmp;
	}
	
	printf("%d\n", solve(w - sum + 1, n));
	
	return 0;
}