#include <bits/stdc++.h>
using namespace std;
int v1, v2, n, m, valor = 1;
int a, b, c;
vector<int> adj[510];
char carac[510];
bool possivel = true;
void ms(int v) {
  for (int i = 1; i <= n; i++) {
    if (adj[i].size() == n - 1)
      carac[i] = 'b', b++;
    else
      carac[i] = 'o';
  }
}
char caracterCorrespondente(int v) {
  if (valor == 1)
    a++;
  else
    c++;
  return (v == 1 ? 'a' : 'c');
}
void dfs(int v, int valor) {
  carac[v] = caracterCorrespondente(valor);
  for (int i = 0; i < adj[v].size(); i++) {
    int x = adj[v][i];
    if (carac[x] != 'o') continue;
    dfs(x, valor);
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n >> m;
  while (m--) {
    cin >> v1 >> v2;
    adj[v1].push_back(v2);
    adj[v2].push_back(v1);
  }
  ms(-1);
  for (int i = 1; i <= n; i++) {
    if (carac[i] == 'o') dfs(i, valor), valor += 2;
  }
  if (valor > 5) possivel = false;
  for (int i = 1; i <= n; i++) {
    if (carac[i] == 'a' && adj[i].size() != a + b - 1)
      possivel = false;
    else if (carac[i] == 'c' && adj[i].size() != c + b - 1)
      possivel = false;
  }
  if (!possivel)
    cout << "No" << endl;
  else {
    cout << "Yes" << endl;
    for (int i = 1; i <= n; i++) {
      cout << carac[i];
    }
    cout << endl;
  }
  return 0;
}
