#include <algorithm>
#include <iostream>
#include <numeric>
#include <queue>
#include <vector>
using namespace std;
using ll = long long;
#define rep(i, j, n) for (int i = j; i < (n); ++i)
#define rrep(i, j, n) for (int i = (n)-1; j <= i; --i)
#define all(a) a.begin(), a.end()
template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> &a) {
  for (size_t i = 0; i < a.size(); ++i) os << (i > 0 ? " " : "") << a[i];
  return os << '\n';
}
template <typename T>
std::istream &operator>>(std::istream &is, std::vector<T> &a) {
  for (T &x : a) { is >> x; }
  return is;
}

[[maybe_unused]] static constexpr long long MOD = 998244353;
[[maybe_unused]] static constexpr int INF = 0x3f3f3f3f;
[[maybe_unused]] static constexpr long long INFL = 0x3f3f3f3f3f3f3f3fLL;

int main() {
  cin.tie(0)->sync_with_stdio(0);
  int n, k;
  cin >> n >> k;
  vector<pair<int, char>> ps;
  rep(i, 0, k) {
    char c;
    int x;
    cin >> x >> c;
    ps.emplace_back(x, c);
  }
  sort(all(ps));
  string ans;
  int cnt[3] = {0, 0, 0};
  bool bad = false;
  for (auto [x, c] : ps) {
    // 1 R, 3 G , 5 B
    // R
    int y = c % 3;
    int z = (y + 1) % 3, w = (y + 2) % 3;
    int mx = (x + 1) / 2;
    while (ans.size() < n &&
           (cnt[y] < mx || cnt[y] < cnt[z] || cnt[y] < cnt[w])) {
      ans += c;
      ++cnt[y];
      if (ans.size() > x) {
        bad = true;
        break;
      }
    }
    if (bad) break;
  }
  while (ans.size() < n) ans += 'R';
  if (bad)
    cout << -1 << '\n';
  else {
    cout << ans << '\n';
  }
}