//ignore header files

int main(int argc, char const* argv[])
{
    int n,k;
    while(scanf("%d %d",&n,&k) != EOF){
        int ans = 1;
        for(int j = 1;j <= n;j++)
            ans = ans*j;
        while(k--){
            int m;
            scanf("%d",&m);
            for(int j = 1;j <= m;j++)
                ans = ans/j;
        }
        printf("%d\n",ans);
    }
    return 0;
}