#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define rd read()
#define pb push_back
#define eb emplace_back
#define f first
#define s second
#define p pair
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/trie_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
namespace {
	typedef long long ll; typedef long double ld; typedef unsigned long long ull; typedef pair<int,int> pii; typedef pair<ll,ll> pll;
//	istream& operator>>(istream& i, ll &v){ long long t; i >> t; v = t;	return i;}
//	ostream& operator<<(ostream& out, ll &v){ 
//		vector<long long> x; ll u = v; 
//		while(u){x.pb(u % 10); u /= 10;} 
//		reverse(x.begin(), x.end()); 
//		for (auto &o : x){out << o;} return out;
//	}
	ll read(){ ll x; cin >> x; return x; } ld PI = 3.14159265358979323846; ld eps = 1e-6; ll mod = 1e9 + 7;
	template<typename T> void Unique(T &a) {a.erase(unique(a.begin(), a.end()), a.end());}
	template<typename T1, typename T2> ostream& operator<<(ostream& out, const p<T1, T2>& x) {return out << x.f << ' ' << x.s;}
	template<typename T1, typename T2> istream& operator>>(istream& in, p<T1, T2>& x) {return in >> x.f >> x.s;}
	template<typename T> istream& operator>>(istream& in, vector<T>& a) {for(auto &x : a) in >> x; return in;};
	template<typename T> ostream& operator<<(ostream& out, vector<T>& a) {for(auto &x : a) out << x << ' '; return out;};
	template<typename T> istream& operator>>(istream& in, deque<T>& a) {for(auto &x : a) in >> x; return in;};
	template<typename T> ostream& operator<<(ostream& out, deque<T>& a) {for(auto &x : a) out << x << ' '; return out;};
	template<typename T> using ordered_set = tree<T, null_type,less<T>, rb_tree_tag,tree_order_statistics_node_update>;
	template<typename T> using ordered_multiset = tree<T, null_type,less_equal<T>, rb_tree_tag,tree_order_statistics_node_update>;
	template<typename T> using pq = priority_queue<T>; template<typename T> using reverse_pq = priority_queue<T, vector<T>, greater<T> >;
	template<typename T> using matrix = vector<vector<T> >; template<typename T> using rubik = vector<vector<vector<T> > >;
	vector<ll> rdv(int sz) { vector<ll> x(sz); cin >> x;return x; }
	mt19937_64 mrand(chrono::steady_clock::now().time_since_epoch().count());
	const int N = 500 + 5;
} // main template

ll color[30]{}, l[30]{}, lx[30]{}, st[30]{}, got[N]{}, a = 0, b = 0;

void solve(){
	ll n = rd - 1, m = rd; set<ll> save[26], ans[m];
	string fi = ""; b = m;
	for (int i = 0; i < m; i++){
		color[i] = 5; fi += '?';
		for (int j = 0; j < 26; j++){
			save[j].insert(i);
			ans[i].insert(j);
		}
	}
	for (int _ = 0; _ < n; _++){
		string s, t; cin >> s >> t;
		for (int i = 0; i < m; i++){
			if (t[i] == 'G'){ // GREEN
				for (int j = 0; j < 26; j++){
					if (j == s[i] - 'a'){
						continue;
					}
					save[j].erase(i);
					ans[i].erase(j);
				}
				fi[i] = s[i];
				if (!got[i]){
					b--;
				}
				got[i] = 1;
				if (l[s[i] - 'a'] > 0){
					lx[s[i] - 'a'] -= 1;	a--;
				}
				
			} else if (t[i] == 'Y'){ // YELLOW
				lx[s[i] - 'a']++; a++;
				save[s[i] - 'a'].erase(i);
				ans[i].erase(s[i] - 'a');
			} else { // BLACK
				st[s[i] - 'a'] = 1;
				save[s[i] - 'a'].erase(i);
				ans[i].erase(s[i] - 'a');
			}
		}
		for (int i = 0; i < 26; i++){
			l[i] = lx[i];
		}
	}
//	cout << fi << '\n';
//	cout << a << ' ' << b << '\n';
//	for (int i = 0; i < 26; i++){
//		cout << (char)(i + 'a') << ' ' << save[i].size() << '\n';
//	}
	while (true){
		ll x;
		for (int i = 0; i < 26; i++){
			if ((ll)save[i].size() < 1){
				continue;
			}
			if ((ll)save[i].size() == l[i]){
				if (st[i] == 0 && a != b){
					continue;
				}
				for (auto &x : save[i]){
					fi[x] = (char)(i + 'a');
					ans[x].erase(i);
				}
				save[i].clear(); l[i] = 0;
				goto nxt;
			}
		}
		for (int i = 0; i < m; i++){
			if (fi[i] == '?'){
				for (auto &x : ans[i]){
					if (l[x] > 0){
						fi[i] = (char)(x + 'a');
						ans[i].erase(x);
						save[x].erase(i);
						l[x]--; goto nxt;
					}
				}
				x = *ans[i].begin();
				fi[i] = (char)(x + 'a');
				ans[i].erase(x);
				save[x].erase(i);
				goto nxt;
			}
		}
		break;
		nxt:;
//		cout << fi << '\n';
	}
	cout << fi << '\n';
}

signed main(){
    cin.tie(0) -> ios::sync_with_stdio(false);
	for (int i = 1, j = 1; i > 0; i--, j++) {
		solve();
	}
}