#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using cd = complex<double>;
const int max_n = 200500;
vector<int> g[max_n];
vector<int> og[max_n];
vector<int> used(max_n);
bool find_cycles(int x) {
  used[x] = 1;
  for (int i : g[x]) {
    if (used[i] == 1) {
      return true;
    }
    if (!used[i] && find_cycles(i)) {
      return true;
    }
  }
  used[x] = 2;
  return false;
}
vector<int> ts;
void top_sort(int x) {
  used[x] = 1;
  for (int i : g[x]) {
    if (!used[i]) {
      top_sort(i);
    }
  }
  ts.push_back(x);
}
vector<int> dp1(max_n);
void calc_dp1(int x) {
  used[x] = 1;
  dp1[x] = x;
  for (int i : og[x]) {
    if (!used[i]) {
      calc_dp1(i);
    }
    dp1[x] = min(dp1[x], dp1[i]);
  }
}
vector<int> dp2(max_n);
void calc_dp2(int x) {
  used[x] = 1;
  dp2[x] = x;
  for (int i : g[x]) {
    if (!used[i]) {
      calc_dp2(i);
    }
    dp2[x] = min(dp2[x], dp2[i]);
  }
}
int main() {
  cout.precision(20);
  cout << fixed;
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    g[a].push_back(b);
    og[b].push_back(a);
  }
  for (int i = 1; i <= n; i++) {
    if (!used[i]) {
      if (find_cycles(i)) {
        cout << -1;
        return 0;
      }
    }
  }
  fill(used.begin(), used.end(), 0);
  for (int i = 1; i <= n; i++) {
    if (!used[i]) {
      top_sort(i);
    }
  }
  reverse(ts.begin(), ts.end());
  fill(used.begin(), used.end(), 0);
  for (int i = 0; i < n; i++) {
    if (!used[ts[i]]) {
      calc_dp1(ts[i]);
    }
  }
  fill(used.begin(), used.end(), 0);
  for (int i = 0; i < n; i++) {
    if (!used[ts[i]]) {
      calc_dp2(ts[i]);
    }
  }
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    cnt += dp1[i] == i && dp2[i] == i;
  }
  cout << cnt << "\n";
  for (int i = 1; i <= n; i++) {
    cout << (dp1[i] == i && dp2[i] == i ? 'A' : 'E');
  }
}
