#include <bits/stdc++.h>
using namespace std;
int cnt = 0;
vector<int> ans;
vector<vector<int> > adj;
void dfs(int u, int col) {
  if (ans[u] != -1) return;
  ans[u] = col;
  for (int i = 0; i < adj[u].size(); ++i) dfs(adj[u][i], col);
}
char conv(int first) {
  if (first == 0) return 'b';
  if (first == 1) return 'a';
  if (first == 2) return 'c';
}
int main() {
  cout.setf(ios::fixed);
  cout.precision(7);
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  adj = vector<vector<int> >(n);
  vector<int> deg(n, 0);
  for (int asdf = 0; asdf < m; ++asdf) {
    int first, second;
    cin >> first >> second;
    --first;
    --second;
    adj[first].push_back(second);
    adj[second].push_back(first);
    ++deg[first];
    ++deg[second];
  }
  ans = vector<int>(n, -1);
  int qt = 0;
  for (int i = 0; i < n; ++i)
    if (deg[i] == n - 1) {
      ans[i] = 0;
      ++qt;
    }
  for (int i = 0; i < n; ++i)
    if (ans[i] == -1) {
      ++cnt;
      dfs(i, cnt);
    }
  bool ok = true;
  if (cnt >= 3) ok = false;
  int n1 = 0, m1 = 0, n2 = 0, m2 = 0;
  for (int i = 0; i < n; ++i) {
    if (ans[i] == 1) {
      ++n1;
      m1 += deg[i] - qt;
    } else if (ans[i] == 2) {
      ++n2;
      m2 += deg[i] - qt;
    }
  }
  if (n1 * (n1 - 1) != m1) ok = false;
  if (n2 * (n2 - 1) != m2) ok = false;
  if (not ok)
    cout << "No\n";
  else {
    cout << "Yes\n";
    for (int i = 0; i < n; ++i) cout << conv(ans[i]);
    cout << '\n';
  }
}
