#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

vector<string> str;

struct node
{
	map<string, int> m;
	map<int, int> ans;
	int sz;
	int mx;
} trie[200500];
int nx = 1;

vector<string> f(string s)
{
	stringstream ss(s);
	vector<string> vs;
	while (!ss.eof())
	{
		string t;
		ss >> t;
		vs.PB(t);
	}
	return vs;
}

void add(string q, string a)
{
	vector<string> vs = f(q);
	int idx = lower_bound(ALL(str), a) - str.begin();
	int v = 0;
	FOR(i, 0, SZ(vs))
	{
		trie[v].ans[idx]++;
		trie[v].mx = max(trie[v].mx, trie[v].ans[idx]);
		trie[v].sz++;
		if (trie[v].m.count(vs[i]))
			v = trie[v].m[vs[i]];
		else
		{
			trie[v].m[vs[i]] = nx;
			v = nx++;
		}
	}
	trie[v].sz = 1;
	trie[v].ans[idx]++;
	trie[v].mx = max(trie[v].mx, trie[v].ans[idx]);
}

void solve()
{
	int tt, n;
	cin >> tt >> n;
	vector<pair<string, string>> to_add;
	FOR(i, 0, n)
	{
		string s;
		if (i == 0) getline(cin, s);
		getline(cin, s);
		int j = s.find('?');
		string q = s.substr(0, j);
		string a = s.substr(j + 1, SZ(s) - j - 1);
		to_add.PB({q, a});
		str.PB(a);
	}
	sort(ALL(str));
	for (auto [q, a] : to_add)
	{
		add(q, a);
	}
	vector<vector<double>> dp(tt + 1, vector<double>(nx));
	FOR(t, 1, tt + 1)
	{
		FOR(v, 0, nx)
		{
			double val1 = double(trie[v].mx) / trie[v].sz + dp[t - 1][0];
			double val2 = 0;
			for (auto [st, to] : trie[v].m)
			{
				val2 += double(trie[to].sz) / trie[v].sz * dp[t - 1][to];
			}
			dp[t][v] = max(val1, val2);
		}
	}
	cout << fixed << setprecision(10) << dp[tt][0] << '\n';
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int t = 1;
	//cin >> t;
	while (t--)
	{
		solve();
	}
	return 0;
}