#include <bits/stdc++.h>
using namespace std;
using namespace std;
template <typename T, typename U>
std::istream& operator>>(std::istream& i, pair<T, U>& p) {
  i >> p.first >> p.second;
  return i;
}
template <typename T>
std::istream& operator>>(std::istream& i, vector<T>& t) {
  for (auto& v : t) {
    i >> v;
  }
  return i;
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& o, const pair<T, U>& p) {
  o << p.first << ' ' << p.second;
  return o;
}
template <typename T>
std::ostream& operator<<(std::ostream& o, const vector<T>& t) {
  if (t.empty()) o << '\n';
  for (size_t i = 0; i < t.size(); ++i) {
    o << t[i] << " \n"[i == t.size() - 1];
  }
  return o;
}
template <typename T>
using minheap = priority_queue<T, vector<T>, greater<T>>;
template <typename T>
using maxheap = priority_queue<T, vector<T>, less<T>>;
template <typename T>
bool in(T a, T b, T c) {
  return a <= b && b < c;
}
unsigned int logceil(int x) {
  return (unsigned int)(8 * sizeof(int) - __builtin_clz(x));
}
namespace std {
template <typename T, typename U>
struct hash<pair<T, U>> {
  hash<T> t;
  hash<U> u;
  size_t operator()(const pair<T, U>& p) const {
    return t(p.x) ^ (u(p.y) << 7);
  }
};
}  // namespace std
template <typename T>
T gcd(T a, T b) {
  if (a < b) swap(a, b);
  return b ? gcd(b, a % b) : a;
}
template <typename T>
class vector2 : public vector<vector<T>> {
 public:
  vector2() {}
  vector2(size_t a, size_t b, T t = T())
      : vector<vector<T>>(a, vector<T>(b, t)) {}
};
template <typename T>
class vector3 : public vector<vector2<T>> {
 public:
  vector3() {}
  vector3(size_t a, size_t b, size_t c, T t = T())
      : vector<vector2<T>>(a, vector2<T>(b, c, t)) {}
};
template <typename T>
class vector4 : public vector<vector3<T>> {
 public:
  vector4() {}
  vector4(size_t a, size_t b, size_t c, size_t d, T t = T())
      : vector<vector3<T>>(a, vector3<T>(b, c, d, t)) {}
};
template <typename T>
class vector5 : public vector<vector4<T>> {
 public:
  vector5() {}
  vector5(size_t a, size_t b, size_t c, size_t d, size_t e, T t = T())
      : vector<vector4<T>>(a, vector4<T>(b, c, d, e, t)) {}
};
void fastIO() { ios::sync_with_stdio(false); }
int n, m;
const int MAXN = 200200;
vector<vector<int>> g;
vector<vector<int>> rg;
int color[MAXN];
bool dfs(int v) {
  if (color[v] == 1) return false;
  if (color[v] == 2) return true;
  color[v] = 1;
  for (auto c : g[v])
    if (!dfs(c)) return false;
  color[v] = 2;
  return true;
}
bool wasf[MAXN], wasb[MAXN], was[MAXN];
void mark(int v, vector<vector<int>>& cg, bool* wasd) {
  if (wasd[v]) return;
  wasd[v] = true;
  was[v] = true;
  for (auto c : cg[v]) mark(c, cg, wasd);
}
class CZadachaProKvantori {
 public:
  void solve(std::istream& in, std::ostream& out) {
    in >> n >> m;
    rg = g = vector<vector<int>>(n);
    int a, b;
    for (int i = (0); i < (m); ++i) {
      in >> a >> b;
      --a;
      --b;
      g[a].push_back(b);
      rg[b].push_back(a);
    }
    memset(color, 0, sizeof(color));
    for (int i = (0); i < (n); ++i) {
      if (!dfs(i)) {
        out << -1 << endl;
        return;
      }
    }
    memset(was, false, sizeof(was));
    memset(wasf, false, sizeof(wasf));
    memset(wasb, false, sizeof(wasb));
    string ans(n, 'E');
    int ac = 0;
    for (int i = (0); i < (n); ++i) {
      if (!was[i]) {
        ans[i] = 'A';
        ac++;
      }
      mark(i, g, wasf);
      mark(i, rg, wasb);
    }
    out << ac << '\n' << ans << endl;
  }
};
int main() {
  CZadachaProKvantori solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  cerr << 1.0 * clock() / CLOCKS_PER_SEC << endl;
  return 0;
}
