#include <bits/stdc++.h>
using namespace std;
const int N = 505;
int n, m;
string ans;
set<int> s[N];
bool check() {
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      int k = abs(ans[i - 1] - ans[j - 1]);
      if (k <= 1 && s[i].find(j) == s[i].end()) {
        return false;
      } else if (k == 2 && s[i].find(j) != s[i].end()) {
        return false;
      }
    }
  }
  return true;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m;
  ans.resize(n, 'a');
  for (int i = 1; i <= n; i++) s[i].insert(i);
  for (int i = 1; i <= m; i++) {
    int u, v;
    cin >> u >> v;
    s[u].insert(v);
    s[v].insert(u);
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (s[i].find(j) == s[i].end()) {
        for (int x = 1; x <= n; x++) {
          if (s[i] == s[x])
            ans[x - 1] = 'a';
          else if (s[j] == s[x])
            ans[x - 1] = 'c';
          else
            ans[x - 1] = 'b';
        }
        if (check()) {
          cout << "Yes" << '\n';
          cout << ans << '\n';
          return 0;
        }
        cout << "No" << '\n';
        return 0;
      }
    }
  }
  cout << "Yes" << '\n';
  cout << ans << '\n';
  return 0;
}
