#include <iostream>

using namespace std;

int total_item;
int conflict;
int a[450];
int b[450];
int res;
void dfs(int index)
{
    if (index > total_item)
    {
        return;
    }
    int flag = 0;
    for (int i = index; i <= total_item; i++)
    {
        for (int j = 1; j <= conflict; j++)
        {
            if (a[j] == index && b[j] == i)
            {
                flag = 1;
                break;
            }
        }
        if (flag == 1)
        {
            flag = 0;
            continue;
        }
        else
        {
            res++;
            dfs(i + 1);
        }
    }
}
int main()
{
    cin >> total_item >> conflict;
    for (int i = 1; i <= conflict; i++)
    {
        cin >> a[i] >> b[i];
    }
    dfs(1);
    cout << res + 1 << endl;
    return 0;
}