#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 7;
vector<int> g[507];
bool is[507][507];
string res;
void no() {
  cout << "No" << endl;
  exit(0);
}
void f(char a, char b) {
  int nd = 0, eg = 0;
  for (int i = 1; i < res.size(); i++) {
    if (res[i] != a && res[i] != b) continue;
    nd++;
    for (int v : g[i]) {
      string s;
      if (res[v] == a || res[v] == b) eg++;
      s += res[i];
      s += res[v];
      if (s == "ac" || s == "ca") no();
    }
  }
  if ((nd * (nd - 1)) != eg) no();
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int T;
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
    is[u][v] = is[v][u] = 1;
  }
  res = string(n + 1, 'c');
  for (int i = 1; i <= n; i++) {
    if (g[i].size() == n - 1) res[i] = 'b';
  }
  for (int i = 1; i <= n; i++) {
    if (res[i] == 'c') {
      res[i] = 'a';
      for (int v : g[i]) {
        if (res[v] == 'c') res[v] = 'a';
      }
      break;
    }
  }
  f('a', 'b');
  f('b', 'c');
  cout << "Yes\n" << res.substr(1) << endl;
  return 0;
}
