#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <set>
#include <map>

//#include "optimization.h"
#include <unordered_map>

#include <cassert>
#include <cstdio>
#include <algorithm>


using namespace std;
int n, m;
vector<bool> mark;
vector<int> comp;
vector<vector<int>> graph;
vector<vector<int>> graph2;
vector<int> order;


void dfs1(int v) {
    mark[v] = true;
    for (auto u: graph[v]) {
        if (!mark[u]) dfs1(u);
    }
    order.push_back(v);
}

void dfs2(int v, int cc) {
    comp[v] = cc;
    for (auto u: graph2[v]) {
        if (comp[u] == -1) {
            dfs2(u, cc);
        }
    }
}

int main() {

    cin >> n >> m;
    vector<vector<char>> color(2, vector<char>(n));
    for (int i = 0; i < n; i++){
        char tmp;
        cin >> tmp;
        if (tmp == 'R'){
            color[0][i] = 'B';
            color[1][i]= 'G';
        }
        else if (tmp == 'B'){
            color[0][i] = 'R';
            color[1][i]= 'G';
        }
        else{
            color[0][i] = 'R';
            color[1][i]= 'B';
        }
    }
//    vector<bool> x((n+1)*2, 0);
    graph.resize(n * 2, vector<int>(0));
    graph2.resize(n * 2, vector<int>(0));
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--;b--;
        for(int k = 0; k < 2; k++){
            for(int j = 0; j < 2; j++){
                if(color[k][a] == color[j][b]){
                    graph[2 * a + 1 - k].push_back(2 * b + j);
                    graph[2 * b + 1 - j].push_back(2 * a + k);

                    graph2[2 * b + j].push_back(2 * a+ 1 - k);
                    graph2[2 * a + k].push_back(2 * b + 1 - j);
                }
            }
        }
    }

    mark.resize(2 * (n), false);
    for (int i = 0; i < 2 * n; i+=1) {
        if (!mark[i]) dfs1(i);
    }
    comp.resize(2 * (n), -1);
    reverse(order.begin(), order.end());
        int cc = 0;
    for (auto v: order) {
        if (comp[v] == -1) {
            dfs2(v, ++cc);
        }
    }
    for (int i=0; i<n; ++i)
        if (comp[i*2] == comp[i*2+1]) {
            cout << ("Impossible");
            return 0;
        }
    int j = 0;
    for (int i = 0; i < 2*n; i+=2) {
        cout << color[(comp[i + 1] > comp[i])][j++];

    }
    cout << '\n';
}