#include <string.h>
#include <iostream>
#include <cstdio>
#include <ctime>
#include <algorithm>
#include <vector>
#include <set>
#include <cmath>
#include <string>
#include <map>
#include <cassert>
#include <queue>

using namespace std;

#define forn(i, n)  for (int i = 0; i < int(n); i++)

const int N = 25;

int n, m;
vector<int> g[N];
long long z[1 << N];

long long calc(int mask)
{
    if (z[mask] > -1)
        return z[mask];
    if (mask == 0)
        return (z[mask] = 0);
    int pos = -1;
    forn(i, n)
        if (mask & (1 << i))
            pos = i;
    long long result = calc(mask ^ (1 << pos));
    forn(i, g[pos].size())
    {
        int j = g[pos][i];
        if (mask & (1 << j))
            result = max(result, 1 + calc(mask ^ (1 << pos) ^ (1 << j)));
    }
    return (z[mask] = result);
}

int main()
{
    cin >> n >> m;
    forn(i, m)
    {
        int a, b;
        cin >> a >> b;
        g[a - 1].push_back(b - 1);
        g[b - 1].push_back(a - 1);
    }
    memset(z, -1, sizeof(z));
    cout << calc((1 << n) - 1) << endl;
    return 0;
}