#include <bits/stdc++.h>
using namespace std;
constexpr long long mod = 1000000007;
const long long INF = mod * mod;
const long double eps = 1e-12;
const long double pi = acos(-1.0);
long long mod_pow(long long a, long long n, long long m = mod) {
  a %= m;
  long long res = 1;
  while (n) {
    if (n & 1) res = res * a % m;
    a = a * a % m;
    n >>= 1;
  }
  return res;
}
struct modint {
  long long n;
  modint() : n(0) { ; }
  modint(long long m) : n(m) {
    if (n >= mod)
      n %= mod;
    else if (n < 0)
      n = (n % mod + mod) % mod;
  }
  operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint &a, modint b) {
  a.n += b.n;
  if (a.n >= mod) a.n -= mod;
  return a;
}
modint operator-=(modint &a, modint b) {
  a.n -= b.n;
  if (a.n < 0) a.n += mod;
  return a;
}
modint operator*=(modint &a, modint b) {
  a.n = ((long long)a.n * b.n) % mod;
  return a;
}
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, int n) {
  if (n == 0) return modint(1);
  modint res = (a * a) ^ (n / 2);
  if (n % 2) res = res * a;
  return res;
}
long long inv(long long a, long long p) {
  return (a == 1 ? 1 : (1 - p * inv(p % a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }
const int max_n = 1 << 18;
modint fact[max_n], factinv[max_n];
void init_f() {
  fact[0] = modint(1);
  for (int i = 0; i < max_n - 1; i++) {
    fact[i + 1] = fact[i] * modint(i + 1);
  }
  factinv[max_n - 1] = modint(1) / fact[max_n - 1];
  for (int i = max_n - 2; i >= 0; i--) {
    factinv[i] = factinv[i + 1] * modint(i + 1);
  }
}
modint comb(int a, int b) {
  if (a < 0 || b < 0 || a < b) return 0;
  return fact[a] * factinv[b] * factinv[a - b];
}
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
struct graph {
 private:
  int n;
  vector<vector<int>> G, rG;
  vector<bool> used;
  vector<int> vs;
  int mk;
  vector<vector<int>> fG;
  vector<vector<int>> ori;
  vector<int> trans;

 public:
  graph(int sz) {
    n = sz;
    G.resize(n);
    rG.resize(n);
    used.resize(n);
    fG.resize(n);
    trans.resize(n, -1);
    ori.resize(n);
  }
  void add_edge(int a, int b) {
    G[a].push_back(b);
    rG[b].push_back(a);
  }
  void dfs(int v) {
    used[v] = true;
    for (int i = 0; i < G[v].size(); i++) {
      if (!used[G[v][i]]) dfs(G[v][i]);
    }
    vs.push_back(v);
  }
  void rdfs(int v, int k) {
    used[v] = true;
    queue<int> q;
    q.push(v);
    vector<int> c;
    while (!q.empty()) {
      int id = q.front();
      q.pop();
      ori[k].push_back(id);
      for (int j = 0; j < rG[id].size(); j++) {
        int to = rG[id][j];
        if (used[to]) {
          if (trans[to] >= 0) c.push_back(trans[to]);
          continue;
        }
        used[to] = true;
        q.push(to);
      }
    }
    sort(c.begin(), c.end());
    int len = unique(c.begin(), c.end()) - c.begin();
    for (int i = 0; i < len; i++) {
      fG[c[i]].push_back(k);
    }
    for (int i = 0; i < ori[k].size(); i++) {
      trans[ori[k][i]] = k;
    }
  }
  void scc() {
    fill(used.begin(), used.end(), false);
    for (int i = 0; i < n; i++) {
      if (!used[i]) dfs(i);
    }
    fill(used.begin(), used.end(), false);
    int k = 0;
    for (int i = (int)vs.size() - 1; i >= 0; i--) {
      if (!used[vs[i]]) {
        rdfs(vs[i], k);
        k++;
      }
    }
    mk = k;
  }
  bool valid() { return n == mk; }
};
void solve() {
  int n, m;
  cin >> n >> m;
  vector<vector<int>> G(n), rG(n);
  vector<bool> cana(n, true);
  graph g(n);
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    G[a].push_back(b);
    rG[b].push_back(a);
    cana[max(a, b)] = false;
    g.add_edge(a, b);
  }
  g.scc();
  if (!g.valid()) {
    cout << -1 << "\n";
    return;
  }
  string ans;
  ans.resize(n);
  vector<bool> chked(n), rchked(n);
  function<void(int, int)> dfs = [&](int id, bool isr) {
    if (!isr) {
      if (chked[id]) return;
      chked[id] = true;
      cana[id] = false;
      for (int to : G[id]) {
        dfs(to, isr);
      }
    } else {
      if (rchked[id]) return;
      rchked[id] = true;
      cana[id] = false;
      for (int to : rG[id]) {
        dfs(to, isr);
      }
    }
  };
  int cnt = 0;
  for (int i = 0; i < n; i++) {
    if (cana[i]) {
      cnt++;
      ans[i] = 'A';
    } else {
      ans[i] = 'E';
    }
    dfs(i, 0);
    dfs(i, 1);
  }
  cout << cnt << "\n";
  cout << ans << "\n";
}
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  solve();
  char nyaa;
  cin >> nyaa;
  return 0;
}
