#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define fi first
#define se second
#define pp push_back
#define all(x) (x).begin(), (x).end()
#define Ones(n) __builtin_popcount(n)
#define endl '\n'
#define mem(arrr, xx) memset(arrr,xx,sizeof arrr)
#define PI acos(-1)
//#define int long long
#define debug(x) cout << (#x) << " = " << x << endl

void Gamal() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
#ifdef Clion
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}

int dx[] = {+0, +0, -1, +1, +1, +1, -1, -1};
int dy[] = {-1, +1, +0, +0, +1, -1, +1, -1};

const double EPS = 1e-9;
const ll OO = 0X3F3F3F3F3F3F3F3F;
const int N = 500 + 5, INF = INT_MAX, MOD = 1e9 + 7, LOG = 20;

#define rep(aa, bb, cc) for(int aa = bb; aa < cc;aa++)
struct Dinic {
	struct Edge {
		int to, rev;
		ll c, oc;
		ll flow() { return max(oc - c, 0LL); } // if you need flows
	};
	vi lvl, ptr, q;
	vector<vector<Edge>> adj;
	Dinic(int n) : lvl(n), ptr(n), q(n), adj(n) {}
	void addEdge(int a, int b, ll c, ll rcap = 0) {
		adj[a].push_back({b, (int)adj[b].size(), c, c});
		adj[b].push_back({a, (int)adj[a].size() - 1, rcap, rcap});
	}
	ll dfs(int v, int t, ll f) {
		if (v == t || !f) return f;
		for (int& i = ptr[v]; i < (int)adj[v].size(); i++) {
			Edge& e = adj[v][i];
			if (lvl[e.to] == lvl[v] + 1)
				if (ll p = dfs(e.to, t, min(f, e.c))) {
					e.c -= p, adj[e.to][e.rev].c += p;
					return p;
				}
		}
		return 0;
	}
	ll calc(int s, int t) {
		ll flow = 0; q[0] = s;
		rep(L,0,31) do { // 'int L=30' maybe faster for random data
			lvl = ptr = vi((int)q.size());
			int qi = 0, qe = lvl[s] = 1;
			while (qi < qe && !lvl[t]) {
				int v = q[qi++];
				for (Edge e : adj[v])
					if (!lvl[e.to] && e.c >> (30 - L))
						q[qe++] = e.to, lvl[e.to] = lvl[v] + 1;
			}
			while (ll p = dfs(s, t, LLONG_MAX)) flow += p;
		} while (lvl[t]);
		return flow;
	}
	bool leftOfMinCut(int a) { return lvl[a] != 0; }
};



set<int>st[N];
int low[30],hi[30];

void go(){
    string s, pat;
    cin >> s >> pat;
    int n = s.size();
    vector<int>frq(26);
    for (int i = 0; i < n; ++i) {
        if(pat[i] != 'G'){
            st[i].erase(s[i] - 'a');
            if(pat[i] == 'Y')frq[s[i] - 'a']++;
        }
        else {
            st[i].clear();
            st[i].insert(s[i] - 'a');
            frq[s[i] - 'a']++;
        }
    }
    for (int i = 0; i < n; ++i) {
        if(pat[i] == 'B'){
            hi[s[i] - 'a'] = low[s[i] - 'a'] = frq[s[i] - 'a'];
        }
    }
    for (int i = 0; i < 26; ++i) {
        low[i] = max(low[i], frq[i]);
    }
}

void solve() {
    int g,l;
    cin >> g >> l;
    g--;
    for (int i = 0; i < 26; ++i) {
        hi[i] = l;
        for (int j = 0; j < l; ++j) {
            st[j].insert(i);
        }
    }

    for (int i = 0; i < g; ++i)go();

    int src = 26 + l,sink = src + 1;
    Dinic flw(sink + 1);

    for (int i = 0; i < l; ++i) {
        flw.addEdge(src,i,1);
        for(auto u:st[i]){
            flw.addEdge(i,u+l,1);
        }
    }

    for (int i = 0; i < 26; ++i) {
        flw.addEdge(i+l,sink,low[i]);
    }

    flw.calc(src,sink);

    for (int i = 0; i < 26; ++i) {
        flw.addEdge(i+l,sink,hi[i]-low[i]);
    }

    flw.calc(src,sink);
    for (int i = 0; i < l; ++i) {
        for(auto &e:flw.adj[i]){
            if(e.flow() && e.to >= l && e.to < l + 26){
                cout << char(e.to - l + 'a');
                break;
            }
        }
    }
}


signed main() {
    Gamal();
    int t = 1;
//    cin >> t;
    while (t--) {
        solve();
    }
}