#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef basic_string<int> BI;
typedef long long ll;
typedef pair<int,int> PII;
typedef double db;
mt19937 mrand(random_device{}()); 
const ll mod=1000000007;
int rnd(int x) { return mrand() % x;}
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll gcd(ll a,ll b) { return b?gcd(b,a%b):a;}
// head

const int N=1201000;
int n,m,z[N];
char s[N];
int fd[N],c[N];
VI f[N],vc[N],g[N];
int find(int x) {
	return fd[x]==x?x:fd[x]=find(fd[x]);
}
int main() {
	scanf("%d%d",&n,&m);
	scanf("%s",s);
	rep(i,0,n) {
		c[i]=(s[i]=='R'?0:(s[i]=='G'?1:2));
	}
	rep(i,0,m) {
		int x,y;
		scanf("%d",&x);
		rep(j,0,x) {
			scanf("%d",&y);
			--y;
			f[i].pb(y);
			g[y].pb(i);
		}
		z[i]=-1;
	}
	rep(i,0,n) if (c[i]!=0&&g[i].empty()) {
		puts("impossible");
		return 0;
	}
	int ans=0;
	auto add=[&](int x,int y,int w) {
		rep(j,0,3) fd[find(3*x+j)]=find(3*y+(w+3-j)%3);
	};
	rep(i,0,3*m) fd[i]=i;
	rep(i,0,n) {
		if (SZ(g[i])==2) {
			int u=g[i][0],v=g[i][1];
			add(u,v,(3-c[i])%3);
		} else if (SZ(g[i])==1) {
			int u=g[i][0];
			add(u,u,2*(3-c[i])%3);
		}
	}
	rep(i,0,3*m) vc[find(i)].pb(i);
	rep(i,0,m) if (z[i]==-1) {
		int mv=1<<30;
		rep(j,0,3) {
			auto zz=vc[find(3*i+j)];
			sort(all(zz));
			bool val=1;
			rep(k,0,SZ(zz)) z[zz[k]/3]=3;
			rep(k,0,SZ(zz)-1) if (zz[k]/3==zz[k+1]/3) {
				val=0;
			}
			int sm=0;
			if (val) {
				rep(k,0,SZ(zz)) sm+=zz[k]%3;
				mv=min(mv,sm);
			}
		}
		if (mv==(1<<30)) {
			puts("impossible");
			return 0;
		}
		ans+=mv;
	}
	printf("%d\n",ans);
}