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#include <iostream>
#include <vector>
#include <string>
#include <bits/stdc++.h>
using namespace std;
struct Clause {
int firstVar;
int secondVar;
};
struct Vertex {
int index;
int lowLink;
bool onStack;
};
struct TwoSatisfiability {
int numVars;
int x;
vector<Clause> &clauses;
stack<int> st;
vector<Vertex> vertices;
vector<vector<int> > adj;
TwoSatisfiability(int n, vector<Clause> &clauses) :
numVars(n),
clauses(clauses),
x(0),
vertices(n * 2, {-1, -1, false}),
adj(n * 2, vector<int>())
{
}
bool tarjan(int i, vector<int> &result) {
Vertex &v = vertices[i];
v.index = x;
v.lowLink = x;
v.onStack = true;
st.push(i);
x++;
for (int a : adj[i]) {
Vertex &w = vertices[a];
if (w.index == -1) {
if (!tarjan(a, result)) return false;
v.lowLink = min(v.lowLink, w.lowLink);
} else if (w.onStack) {
v.lowLink = min(v.lowLink, w.index);
}
}
// is a SCC root node
if (v.lowLink == v.index) {
for (;;) {
int i = st.top();
int iv = inv(i);
if (vertices[iv].index == v.index) return false;
st.pop();
if (i < numVars) {
if (result[i] == -1)
result[i] = 1;
} else {
if (result[iv] == -1)
result[iv] = 0;
}
vertices[i].onStack = false;
if (vertices[i].index == v.index) {
break;
}
}
}
return true;
}
inline int idx(int v) { return (v > 0 ? (v - 1) : (numVars - v - 1)); }
inline int inv(int i) { return i + ((i < numVars) ? numVars : -numVars); }
bool isSatisfiable(vector<int>& result) {
// construct the implication graph (l1 l2) -> !l1 ->l2 !l2->l1
for(Clause clause : clauses) {
adj[idx(-clause.firstVar)].push_back(idx(clause.secondVar));
adj[idx(-clause.secondVar)].push_back(idx(clause.firstVar));
}
// find SCC's of graph
// int x = 0;
for (int i = 0; i < vertices.size(); i++) {
Vertex &v = vertices[i];
if (v.index == -1) {
if (!tarjan(i, result)) return false;
}
}
return true;
}
};
enum Color { R=1, G, B };
static inline int var(int vertex, int color) { return vertex * 3 + color; }
/*
Arguments:
* `n` - the number of vertices.
* `edges` - list of edges, each edge is a pair (u, v), 1 <= u, v <= n.
* `colors` - string consisting of `n` characters, each belonging to the set {'R', 'G', 'B'}.
Return value:
* If there exists a proper recoloring, return value is a string containing new colors, similar to the `colors` argument.
* Otherwise, return value is an empty string.
*/
string assign_new_colors(int n, vector<pair<int, int>> edges, string colors) {
// cout << " N : " << n << endl;
// cout << " edges : " << edges.size() << endl;
// cout << " colors : " << colors << endl;
int vars = 3 * n;
vector<Clause> clauses;
// for each vertex
for (int i = 0; i < n; i++) {
// each node must be of a different color than its initial state
int v1, v2, v3;
if (colors[i] == 'R') {
v1 = var(i, R);
v2 = var(i, G);
v3 = var(i, B);
} else if (colors[i] == 'G') {
v1 = var(i, G);
v2 = var(i, B);
v3 = var(i, R);
} else {
v1 = var(i, B);
v2 = var(i, R);
v3 = var(i, G);
}
clauses.push_back({-v1, -v1}); // !1 || !1 => different from initial color
clauses.push_back({ v2, v3}); // 2 || 3 => one of the other
clauses.push_back({-v2, -v3}); // !2 || !3 => not both
}
// both node of an edge cannot be of the same color
for (auto &p : edges) {
int i = p.first - 1;
int j = p.second - 1;
clauses.push_back({-var(i, R), -var(j, R)});
clauses.push_back({-var(i, G), -var(j, G)});
clauses.push_back({-var(i, B), -var(j, B)});
}
// cout << "clauses : " << clauses.size() << endl;
// cout << "vars : " << vars << endl;
TwoSatisfiability twoSat(vars, clauses);
vector<int> result(vars, -1);
if (twoSat.isSatisfiable(result)) {
// cout << "SATISFIABLE" << endl;
// for (int i = 1; i <= vars; ++i) {
// if (result[i-1]) {
// cout << i;
// } else {
// cout << -i;
// }
// if (i < vars) {
// cout << " ";
// } else {
// cout << endl;
// }
// }
string new_colors;
for (int i = 0; i < vars; ++i) {
if (result[i]) {
new_colors.push_back("RGB"[i % 3]);
}
}
return new_colors;
} else {
return "";
}
}
int main() {
int n, m;
cin >> n >> m;
string colors;
cin >> colors;
vector<pair<int, int> > edges;
for (int i = 0; i < m; i++) {
int u, v;
cin >> u >> v;
edges.push_back(make_pair(u, v));
}
string new_colors = assign_new_colors(n, edges, colors);
if (new_colors.empty()) {
cout << "Impossible";
} else {
cout << new_colors << endl;
}
}
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