#include <bits/stdc++.h>
using namespace std;
int n, m;
vector<vector<int> > graph;
vector<char> ans;
vector<int> s(2, 0);
bool B = true;
void searcha(int i, char c, char other) {
  ans[i] = c;
  if (c == 'a')
    s[0] = ((int)(graph[i]).size());
  else
    s[1] = ((int)(graph[i]).size());
  for (int j = 0; j < ((int)(graph[i]).size()); ++j) {
    if (ans[graph[i][j]] == 'd')
      ans[graph[i][j]] = c;
    else if (ans[graph[i][j]] == other) {
      B = false;
      break;
    }
  }
}
void searcha(int i) {
  s[0] = ((int)(graph[i]).size());
  for (int j = 0; j < ((int)(graph[i]).size()); ++j) {
    if (ans[graph[i][j]] == 'd') ans[graph[i][j]] = 'a';
  }
}
int main() {
  cin >> n >> m;
  ans = vector<char>(n, 'd');
  graph = vector<vector<int> >(n, vector<int>(0));
  int a, b1;
  for (int i = 0; i < m; ++i) {
    cin >> a >> b1;
    --a;
    --b1;
    graph[a].push_back(b1);
    graph[b1].push_back(a);
  }
  for (int i = 0; i < n; ++i) {
    if (((int)(graph[i]).size()) == n - 1) {
      ans[i] = 'b';
    }
  }
  bool f = true;
  bool f1 = true;
  for (int i = 0; i < n; ++i) {
    if (ans[i] != 'b' and B) {
      if (f) {
        searcha(i, 'a', 'c');
        f = false;
      } else if (ans[i] == 'a') {
        if (((int)(graph[i]).size()) != s[0]) {
          B = false;
          break;
        }
      } else if (f1) {
        searcha(i, 'c', 'a');
        f1 = false;
      } else if (ans[i] == 'c') {
        if (((int)(graph[i]).size()) != s[1]) {
          B = false;
          break;
        }
      } else if (not(f or f1)) {
        if (ans[i] == 'd') {
          B = false;
          break;
        }
      }
    }
  }
  if (B) {
    cout << "Yes" << endl;
    for (int i = 0; i < n; ++i) cout << ans[i];
  } else
    cout << "No";
  cout << endl;
}
