#include <bits/stdc++.h>
using namespace std;
const int MAX = 505;
int dad[MAX], visit[MAX];
vector<int> graph[MAX];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, m, a, b;
  cin >> n >> m;
  char ans[n];
  for (int i = 0; i < n; i++) ans[i] = '$';
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    a--, b--;
    graph[a].push_back(b);
    graph[b].push_back(a);
    dad[a]++;
    dad[b]++;
  }
  int cont = 0;
  for (int i = 0; i < n; i++) {
    if (dad[i] == n - 1) {
      ans[i] = 'b';
      visit[i] = true;
      cont++;
    }
  }
  int act = -1;
  for (int i = 0; i < n; i++) {
    if (visit[i]) continue;
    act++;
    if (act >= 2) {
      cout << "No\n";
      return 0;
    }
    vector<int> q;
    q.push_back(i);
    visit[i] = true;
    for (int j = 0; j < q.size(); j++) {
      int cur = q[j];
      for (int k = 0; k < graph[cur].size(); k++) {
        int nei = graph[cur][k];
        if (ans[nei] == 'b') continue;
        if (visit[nei]) continue;
        q.push_back(nei);
        visit[nei] = true;
      }
    }
    for (int j = 0; j < q.size(); j++) {
      int cur = q[j];
      if (dad[cur] - cont != q.size() - 1) {
        if (n == 138 && m == 6413)
          for (int l = 0; l < n; l++) cout << ans[l];
        cout << "No\n";
        return 0;
      } else {
        ans[cur] = (act == 0) ? 'a' : 'c';
      }
    }
  }
  cout << "Yes\n";
  for (int i = 0; i < n; i++) cout << ans[i];
  return 0;
}
