#include <bits/stdc++.h>
using namespace std;
long long mod = 1000000007;
long long mod2 = 998244353;
long long mod3 = 1000003;
long long mod4 = 998244853;
long long mod5 = 1000000009;
long long inf = 1LL << 62;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-14;
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
long long gcd(long long a, long long b) {
  if (a < b) swap(a, b);
  if (b == 0) return a;
  if (a % b == 0) return b;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) {
  long long c = gcd(a, b);
  return a * b / c;
}
long long Pow(long long n, long long k) {
  long long ret = 1;
  long long now = n;
  while (k > 0) {
    if (k & 1) ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
long long beki(long long n, long long k, long long md) {
  long long ret = 1;
  long long now = n;
  now %= md;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
long long gyaku(long long n, long long md) { return beki(n, md - 2, md); }
long long popcount(long long n) {
  long long ret = 0;
  long long u = n;
  while (u > 0) {
    ret += u % 2;
    u /= 2;
  }
  return ret;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<int> v[n], w[n];
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    v[a].push_back(b);
    w[b].push_back(a);
  }
  queue<int> qq;
  for (int i = 0; i < n; i++) {
    if (v[i].size() == 0) qq.push(i);
  }
  int cnt = 0;
  int noko[n];
  for (int i = 0; i < n; i++) noko[i] = v[i].size();
  while (qq.size() > 0) {
    int now = qq.front();
    qq.pop();
    cnt++;
    for (int i = 0; i < w[now].size(); i++) {
      int ne = w[now][i];
      noko[ne]--;
      if (noko[ne] == 0) qq.push(ne);
    }
  }
  if (cnt < n) {
    cout << -1 << endl;
    return 0;
  }
  int ans[n];
  bool used[n];
  fill(used, used + n, false);
  bool used2[n];
  fill(used2, used2 + n, false);
  int cn = 0;
  for (int i = 0; i < n; i++) {
    if (used[i] == false && used2[i] == false) {
      ans[i] = 1;
      cn++;
    } else
      ans[i] = 0;
    if (used[i] == false) {
      used[i] = true;
      queue<int> q;
      q.push(i);
      while (q.size() > 0) {
        int now = q.front();
        q.pop();
        for (int j = 0; j < v[now].size(); j++) {
          int ne = v[now][j];
          if (used[ne]) continue;
          used[ne] = true;
          q.push(ne);
        }
      }
    }
    if (used2[i] == false) {
      used2[i] = true;
      queue<int> q;
      q.push(i);
      while (q.size() > 0) {
        int now = q.front();
        q.pop();
        for (int j = 0; j < w[now].size(); j++) {
          int ne = w[now][j];
          if (used2[ne]) continue;
          used2[ne] = true;
          q.push(ne);
        }
      }
    }
  }
  cout << cn << endl;
  for (int i = 0; i < n; i++) {
    if (ans[i] == 0)
      cout << "E";
    else
      cout << "A";
  }
  cout << endl;
}
