#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 1;
int n, m, tin[N], up[N], dw[N];
bool ans[N];
vector<int> edge[N], redge[N];
void topo() {
  queue<int> q;
  for (int i = 1; i <= n; i++)
    if (!tin[i]) q.push(i);
  while (q.size()) {
    int at = q.front();
    q.pop();
    for (auto to : edge[at])
      if (!--tin[to]) q.push(to);
  }
}
void dfs2(int at, int rt, int rev) {
  if (!rev) {
    up[at] = rt;
    for (auto to : edge[at])
      if (!up[to]) dfs2(to, rt, rev);
  } else {
    dw[at] = rt;
    for (auto to : redge[at])
      if (!dw[to]) dfs2(to, rt, rev);
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    edge[x].push_back(y);
    redge[y].push_back(x);
    tin[y]++;
  }
  topo();
  int ok = 1;
  for (int i = 1; i <= n; i++)
    if (tin[i]) ok = 0;
  if (!ok)
    cout << -1 << '\n';
  else {
    for (int i = 1; i <= n; i++) {
      if (!up[i]) dfs2(i, i, 0);
      if (!dw[i]) dfs2(i, i, 1);
    }
    int cnt = 0;
    for (int i = 1; i <= n; i++)
      if (up[i] == i and dw[i] == i) ans[i] = 1, cnt++;
    cout << cnt << '\n';
    for (int i = 1; i <= n; i++) cout << (ans[i] ? 'A' : 'E');
    cout << '\n';
  }
}
