#include <bits/stdc++.h>
using namespace std;
bool tab[500][500];
char slowo[500];
int main() {
  ios_base::sync_with_stdio(0);
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; i++) slowo[i] = 'x';
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    tab[a][b] = tab[b][a] = 1;
  }
  for (int i = 0; i < n; i++) {
    int ile = 0;
    bool z_a = 0, z_c = 0;
    for (int j = 0; j < n; j++) {
      if (i == j) continue;
      if (tab[i][j]) ile++;
      if (!tab[i][j] && slowo[j] == 'a') z_a = 1;
      if (!tab[i][j] && slowo[j] == 'c') z_c = 1;
    }
    if (ile == n - 1) {
      slowo[i] = 'b';
      continue;
    }
    if (z_a && z_c) {
      cout << "No\n";
      return 0;
    }
    if (z_a)
      slowo[i] = 'c';
    else
      slowo[i] = 'a';
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (i == j) continue;
      if ((slowo[i] == 'a' && slowo[j] == 'c') ||
          (slowo[i] == 'c' && slowo[j] == 'a')) {
        if (tab[i][j] == 1) {
          cout << "No\n";
          return 0;
        }
      } else {
        if (tab[i][j] == 0) {
          cout << "No\n";
          return 0;
        }
      }
    }
  }
  cout << "Yes\n";
  for (int i = 0; i < n; i++) cout << slowo[i];
  cout << "\n";
}
