#include <iostream>
#include <vector>

#define MOD 1e9+7

using namespace std;

int main()
{
    int n, m;
    cin >> n >> m;

    vector<int>oks(n+1, 1);
    for (int i = 0; i < m; ++i) {
        int a; cin >> a;
        oks[a] = false;
    }

    vector<long long int>dp(n+1);
    dp[0] = 1;
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j <= min(n, i + 2); ++i) {
            if (oks[j]) {
                dp[j] += dp[i];
            }
        }
    }

    cout << dp[N] << endl;
    return 0;
}