#include "bits/stdc++.h"

using namespace std;

// tests the case which node has color c
bool test(vector<int> &colors, vector<int> buttons[], vector<int> buttonsinv[], int node, int c, vector<int> &buttonans, unordered_set<int> &lightlist, unordered_set<int> &buttonlist) {
    // cout << "> test node " << node << " with color " << c << endl;

    // se o valor do botao for diferente do que ja foi determinado para ele
    if(buttonlist.find(node) != buttonlist.end() && buttonans[node] != c) {
        // cout << ">> bad 1 : " << buttonans[node] << " " << c << endl;
        return false;
    }

    buttonans[node] = c;
    buttonlist.insert(node);
    
    for(auto &light: buttons[node]) {
        if(lightlist.find(light) != lightlist.end()) continue;
        lightlist.insert(light);

        // cout << "> light " << light << " size " << buttonsinv[light].size() << endl;

        // se esse for o unico botao da lampada, tem que ir pro 0
        if(buttonsinv[light].size() == 1) {
            // cout << "only 1 : " << (colors[light] + c) << endl;
            if((colors[light] + c) % 3 != 0) {
                // cout << ">> bad 2 : " << colors[light] << " " << c << endl;
                return false;
            }
        }

        // se esse for um dos botoes, precisa seguir com o valor restante
        else {
            int cnext = (3 - (colors[light] + c) % 3) % 3;
            int buttonnext = (buttonsinv[light][0] == node) ? buttonsinv[light][1] : buttonsinv[light][0];
            // cout << "cnext " << cnext << " buttonnext " << buttonnext << " | " << buttonsinv[light][0] << " " << buttonsinv[light][1] << endl;
            bool r = test(colors, buttons, buttonsinv, buttonnext, cnext, buttonans, lightlist, buttonlist);
            if(r == false) return false;
        }
    }

    return true;
}

int main(){
    int l, b;
    cin >> l >> b;

    vector<int> colors(l);
    for(int i=0; i<l; i++) {
        char c; cin >> c;
        if(c == 'R') colors[i] = 0;
        if(c == 'G') colors[i] = 1;
        if(c == 'B') colors[i] = 2;
    }

    vector<int> buttons[b], buttonsinv[l];
    for(int i=0; i<b; i++) {
        int k; cin >> k;
        for(int j=0; j<k; j++) {
            int v; cin >> v; v--;
            buttons[i].push_back(v);
            buttonsinv[v].push_back(i);
        }
    }

    vector<bool> ok(b, false);
    vector<int> buttonans(b, -1);
    unordered_set<int> globallightlist;
    int resp = 0;
    for(int i=0; i<b; i++) {
        if(ok[i] == true) continue;

        // cout << endl << "FOR " << i << endl << endl;

        int tempresp = 100000000;
        for(int c=0; c<3; c++) {
            unordered_set<int> buttonlist;
            unordered_set<int> lightlist;
            
            bool res = test(colors, buttons, buttonsinv, i, c, buttonans, lightlist, buttonlist);
            if(res == true) {
                int count = 0;
                
                // cout << endl << "good with " << c << endl;
                for(auto j: buttonlist) {
                    // cout << buttonans[j];
                    if(buttonans[j] != -1) {
                        ok[j] = true;
                        count += buttonans[j];
                    }
                }

                tempresp = min(tempresp, count);

                for(auto &v: lightlist)
                    globallightlist.insert(v);
            }
        }

        if(tempresp == 100000000) {
            cout << "impossible" << endl;
            return 0;
        }

        resp += tempresp;
    }

    for(int i=0; i<l; i++) {
        // cout << i << " " << (globallightlist.find(i) == globallightlist.end()) << " " << colors[i] << endl;
        if(globallightlist.find(i) == globallightlist.end() && colors[i] != 0) {
            cout << "impossible" << endl;
            return 0;
        }
    }

    cout << resp << endl;

    return 0;
}