#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}
int dp[100001];
int main() {
  int k = ri(), n = ri();
  int a[n];
  for (int i = 0; i < n; i++) a[i] = -ri();
  dp[0] = 1;
  int start = 0;
  for (int i = 1; i <= k; i++) {
    int64_t cur = 0;
    while (start < n && -a[start] <= i) start++;
    int *src = dp + i;
    for (int j = 0; j < start; j++)
      cur += src[a[j]];
    dp[i] = cur % 1000000007;
  }
  std::cout << dp[k] << std::endl;
  return 0;
}