#include <bits/stdc++.h>
#define pb push_back
#define pii pair<int,int>
#define fi first
#define int long long
#define se second
#define ios ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define TXT "color3"
#define endl cout<<"\n";
#define freo if(fopen(TXT".inp","r")){freopen(TXT".inp","r",stdin); freopen(TXT".out","w",stdout);}             ///TEMPLATE MADE BY NIETTRAAN
using namespace std;
 
const int MXN = 1005;
vector<int> adj[MXN];
string orig, res;
int n, m;
bool vis[MXN];
 
vector<int> comp;
 
bool bfs_component(int start) {
    comp.clear();
    queue<int> q;
    q.push(start);
    vis[start] = 1;
    comp.pb(start);
    while(!q.empty()) {
        int u = q.front(); q.pop();
        for(int v : adj[u]) {
            if(!vis[v]) {
                vis[v] = 1;
                q.push(v);
                comp.pb(v);
            }
        }
    }
 
    // thử 3 màu gốc
    for(char startColor : {'R','G','B'}) {
        if (startColor == orig[start]) continue; // phải khác màu cũ
        map<int,char> color;
        queue<int> qq;
        qq.push(start);
        color[start] = startColor;
 
        bool ok = true;
        while(!qq.empty() && ok) {
            int u = qq.front(); qq.pop();
            for(int v : adj[u]) {
                if(color.count(v)) {
                    if(color[v] == color[u]) {ok=false; break;}
                } else {
                    // tìm màu cho v khác color[u] và khác orig[v]
                    bool found = false;
                    for(char c : {'R','G','B'}) {
                        if(c != color[u] && c != orig[v]) {
                            color[v] = c;
                            found = true;
                            break;
                        }
                    }
                    if(!found){ok=false; break;}
                    qq.push(v);
                }
            }
        }
 
        if(ok) {
            for(auto &x : color) res[x.fi] = x.se;
            return true;
        }
    }
    return false;
}
 
void solve() {
    cin >> n >> m;
    cin >> orig;
    orig = " " + orig;
    res.resize(n+1,' ');
    for(int i=1;i<=m;i++){
        int u,v;cin>>u>>v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
 
    for(int i=1;i<=n;i++){
        if(!vis[i]){
            if(!bfs_component(i)){
                cout << "Impossible\n";
                return;
            }
        }
    }
 
    for(int i=1;i<=n;i++) cout << res[i];
    cout << "\n";
}
 
int32_t main(){
    ios;
    freo;
    solve();
    return 0;
}