#include <bits/stdc++.h>
using namespace std;
const int N = 8e5 + 5; 

int n, m, cnt[N], vis[N]; 
char a[N]; 
vector<int> G[N]; 

int main(void) {
    ios::sync_with_stdio(0); 
    cin >> n >> m >> a + 1; 
    for (int i = 1; i <= n; ++i)
        if (a[i] == 'R') a[i] = 0; 
        else if (a[i] == 'G') a[i] = 1; 
        else a[i] = 2; 
    for (int i = 1; i <= m; ++i) {
        int k; cin >> k; 
        while (k--) {
            int x; cin >> x; 
            G[i].emplace_back(x + m); 
            G[x + m].emplace_back(i); 
        }
    }
    for (int i = 1; i <= n; ++i)
        if (!G[i + m].size() && a[i]) return cout << "impossible\n", 0; 
    int ans = 0; 
    for (int i = 1; i <= m; ++i) if (!vis[i]) {
        int mn = 1e9; 
        vector<int> now; 
        bool flg = 1; 
        auto dfs = [&](auto &&self, int x) -> void {
            vis[x] = 1; now.emplace_back(x); 
            if (x <= m) {
                for (int y : G[x])
                    if (vis[y] != 1) self(self, y); 
            } else {
                int s = a[x - m], p = 0; 
                for (int y : G[x])
                    if (vis[y] != 1) p = y; 
                    else s += cnt[y]; 
                if (p) cnt[p] = (3 - s % 3) % 3, self(self, p);
                else if (s % 3 != 0) flg = 0; 
            }
        }; 
        for (cnt[i] = 0; cnt[i] < 3; ++cnt[i]) {
            flg = 1; dfs(dfs, i); int s = 0; 
            if (flg) { for (int j : now) if (j <= m) s += cnt[j]; mn = min(mn, s); }
            for (int j : now) vis[j] = 2; now.clear(); 
        }
        if (mn == 1e9) return cout << "impossible\n", 0; 
        ans += mn; 
    }
    cout << ans << "\n"; 
    return 0;
}