#include <bits/stdc++.h>
using namespace std;
int n, m;
map<pair<int, int>, bool> is_edge;
vector<int> g[505], h[505];
char s[505];
bool vis[505];
void dfs(int cur) {
  vis[cur] = true;
  for (int v : g[cur]) {
    if (vis[v]) {
      if (s[cur] == s[v]) {
        cout << "No" << endl;
        exit(0);
      }
    } else {
      if (s[cur] == 'a')
        s[v] = 'c';
      else
        s[v] = 'a';
      dfs(v);
    }
  }
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    is_edge[{u, v}] = is_edge[{v, u}] = true;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (!is_edge[{i, j}]) {
        g[i].push_back(j);
        g[j].push_back(i);
      }
    }
  }
  fill(s + 1, s + 1 + n, 'b');
  for (int i = 1; i <= n; i++) {
    if (!vis[i] && g[i].size()) {
      s[i] = 'a';
      dfs(i);
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (s[i] == 'a' && s[j] == 'c' || s[i] == 'c' && s[j] == 'a') {
        h[i].push_back(j);
        h[j].push_back(i);
      }
    }
    if (g[i] != h[i]) {
      cout << "No" << endl;
      return 0;
    }
  }
  cout << "Yes" << endl;
  for (int i = 1; i <= n; i++) cout << s[i];
  cout << endl;
  return 0;
}
