#include <bits/stdc++.h>
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pdd pair<double, double>
#define F first
#define S second 
#define all(x) x.begin(), x.end()
using namespace std;

const ll INF = 1'000'000'000;
int N, M, vis[400005], sol[400005], force[400005];
vector<pii> E[400005];
vector<int> light[200005];
string s;
ll sum = 0, ans = 0, best[400005];

int convert(char c)
{
    if (c == 'R')
        return 0;
    else if (c == 'G')
        return 2;
    else if (c == 'B')
        return 1;
    assert(false);
    return 0;
}

void dfs(int u, int c)
{
    if (sol[u] == -1) sol[u] = c;
    if (force[u] != -1 && force[u] != c)
        sum += INF;
    if (sol[u] != c)
        sum += INF;
    if (vis[u]) return;

    sum += c;
    vis[u] = 1;
    for (auto [v, w] : E[u])
        dfs(v, (w - sol[u] + 3) % 3);
}

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

    cin >> M >> N;
    cin >> s;
    s =  " " + s;
    for (int i = 1; i <= N; i++)
    {
        int j, k;
        cin >> j;
        while (j--)
        {
            cin >> k;
            light[k].emplace_back(i);
        }
    }
    fill(force + 1, force + 1 + N, -1);
    for (int i = 1; i <= M; i++)
    {
        if (light[i].size() == 0)
        {
            if (s[i] != 'R')
                ans = INF;
        }
        else if (light[i].size() == 1)
        {
            if (force[light[i][0]] != convert(s[i]) && force[light[i][0]] != -1)
                ans = INF;
            force[light[i][0]] = convert(s[i]);
        }
        else 
        {
            int u = light[i][0], v = light[i][1];
            E[u].emplace_back(v, convert(s[i]));
            E[v].emplace_back(u, convert(s[i]));
        }
    }
    for (int t = 0; t < 3; t++)
    {   
        fill(sol + 1, sol + 1 + N, -1);
        fill(vis + 1, vis + 1 + N, 0);
        for (int i = 1; i <= N; i++)
            if (!vis[i])
            {
                if (t == 0) best[i] = INF;
                sum = 0;
                dfs(i, t);
                best[i] = min(best[i], sum);
            }
    }
    for (int i = 1; i <= N; i++)
        ans += best[i];
    if (ans >= INF)
        cout << "impossible\n";
    else 
        cout << ans << '\n';
}