#include <bits/stdc++.h>
using namespace std;
int main()
{
	ios_base::sync_with_stdio(false);
	const int inf=0x3f3f3f3f;
	int l,b;
	cin>>l>>b;
	string s;
	vector<int> a(l+5);
	cin>>s;
	s=' '+s;
	for(int i=1;i<=l;i++)
	{
		if(s[i]=='R')a[i]=0;
		else if(s[i]=='G')a[i]=1;
		else a[i]=2;
	}
	//LLLLLLLLLBBBBBBBBBB
	const int N=l+b;
	vector<vector<int>> G(N+5);
	for(int i=1;i<=b;i++)
	{
		int k;
		cin>>k;
		for(int j=1;j<=k;j++)
		{
			int x;
			cin>>x;
			G[i+l].push_back(x);
			G[x].push_back(i+l);
		}
	}
//	cerr<<"?"<<endl;
	vector<int> vis(N+5);
	vector<int> subs;
	function<void(int)> dfs0=[&](int u)
	{
		vis[u]=1;
		subs.push_back(u);
		for(auto v:G[u])
		{
			if(not vis[v])
			{
				dfs0(v);
			}
		}
	};
	vector<int> col(N+5);
	function<int(int,int)> solve=[&](int r,int ty)
	{
//		cerr<<"solve "<<r<<' '<<ty<<endl;
		int ret=0;
		queue<int> q;
		q.push(r);
		vis[r]=1;
		col[r]=ty;
		while(not q.empty())
		{
			int u=q.front();q.pop();
//			cerr<<"test "<<u<<endl;
			ret+=col[u];
			for(auto v:G[u])
			{
				if(not vis[v])
				{
					int need=(6-a[v]-col[u])%3;
					if(G[v].size()==1u and need!=0)return inf;
					for(auto z:G[v])
					{
						if(z!=u)
						{
							if(col[z]!=-1 and col[z]!=need)return inf;
							col[z]=need;
							if(not vis[z])
							{
								q.push(z);
								vis[z]=1;
							}
						}
					}
				}
			}
		}
		return ret;
	};
	int ans=0;
	for(int i=1;i<=b;i++)
	{
		if(not vis[i+l])
		{
			subs.clear();
			dfs0(i+l);
			int minn=inf;
			for(int kk=0;kk<=2;kk++)
			{
				for(auto u:subs)col[u]=-1,vis[u]=0;
				int ret=solve(i+l,kk);
				if(ret<minn)minn=ret;
			}
			for(auto u:subs)col[u]=-1,vis[u]=1;
			if(minn==inf)
			{
				cout<<"impossible"<<endl;
				return 0;
			}
//			cerr<<"ans "<<i<<' '<<minn<<endl;
			ans+=minn;
		}
	}
	for(int i=1;i<=l;i++)
	{
		if(a[i] and G[i].size()==0)
		{
			cout<<"impossible"<<endl;
			return 0;
		}
	}
	cout<<ans<<endl;
	return 0;
}