#include <bits/stdc++.h>
#define MULTI \
    int _;    \
    cin >> _; \
    while (_--)
#define fi first
#define se second
#define pb(a) push_back(a)
#define rep(i, n) for (int i = 0; i < n; i++)
#define reps(i, n, m) for (int i = n; i <= m; i++)
#define repsv(i, n, m) for (int i = n; i >= m; i--)
#define vsz(a) (int)(a.size())
#define mp(a, b) make_pair(a, b)
#define all(a) a.begin(), a.end()

using namespace std;

typedef pair<double, double> pdd;
typedef pair<int, int> pii;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef long long int ll;
typedef long double ld;
typedef vector<ll> vll;

#ifdef LOCAL
#include "debugs.hpp"
#else
#define dbg(...) 0
#endif

vi l;
vector<vi> gl, gb;
vector<bool> traite;
vi vul, vub, pressb;

bool dfs1(int b, int presses, int& acc, int pid);
bool dfs2(int i, int presses, int& acc, int pid, int bPrec);

bool dfs1(int b, int presses, int& acc, int pid){
    dbg(b, presses);
    acc += presses;
    vub[b] = pid;
    traite[b] = true;
    pressb[b] = presses;
    for(int i : gb[b]){
        if(vul[i] != pid){
            if(!dfs2(i, presses, acc, pid, b))
                return false;
        }
    }
    return true;
}

bool dfs2(int i, int presses, int& acc, int pid, int bPrec){
    int val = (l[i]+presses)%3;
    vul[i] = pid;
    dbg(i, val);
    if(gl[i].size() == 1){
        dbg("size 1");
        return val == 0;
    }
    int nextPresses = (3-val)%3;
    dbg(nextPresses);
    for(int j : gl[i]){
        dbg(j);
        if(vub[j] != pid){
            if(!dfs1(j, nextPresses, acc, pid))
                return false;
        }
        else if(j != bPrec && pressb[j] != nextPresses)
            return false;
    }
    return true;
}

void solve()
{
    int ln, bn;
    cin >> ln >> bn;
    l = vi(ln);
    gl = vector<vi>(ln);
    gb = vector<vi>(bn);
    rep(i, ln){
        char c;
        cin >> c;
        if(c == 'R') l[i] = 0;
        else if(c == 'G') l[i] = 1;
        else l[i] = 2;
    }
    rep(i, bn){
        int n;
        cin >> n;
        rep(j, n){
            int in;
            cin >> in;
            in--;
            gl[in].pb(i);
            gb[i].pb(in);
        }
    }
    
    rep(i, ln){
        if(gl[i].size() == 0 && l[i] != 0){
            cout << "impossible\n";
            return;
        }
    }

    traite = vector<bool>(bn);
    vul = vi(ln), vub = vi(ln);
    pressb = vi(bn);
    int pid = 0;
    int sum = 0;
    rep(bbase, bn){
        if(traite[bbase]) continue;
        int curbest = INT_MAX;
        rep(i, 3){
            int acc = 0;
            if(dfs1(bbase, i, acc, ++pid)){
                curbest = min(curbest, acc);
            }
        }
        if(curbest == INT_MAX){
            cout << "impossible\n";
            return;
        }
        sum += curbest;
    }
    cout << sum << '\n';
}

int main()
{
    ios_base::sync_with_stdio(false);
    // MULTI
    solve();
}