#include <bits/stdc++.h>
using namespace std;
struct hash_pair {
  template <class T1, class T2>
  size_t operator()(const pair<T1, T2>& p) const {
    auto h1 = hash<T1>{}(p.first);
    auto h2 = hash<T2>{}(p.second);
    return h1 ^ h2;
  }
};
vector<int> adj[501], a, b, c;
vector<char> ans(501, '-');
vector<int> deg(501, 0);
bool adjm[501][501];
void dfs(int node) {
  ans[node] = 'a';
  a.push_back(node);
  for (auto k : adj[node])
    if (ans[k] == '-') dfs(k);
}
bool checker(vector<int> v) {
  for (int i = 0; i < (int)v.size(); i++) {
    for (int j = i + 1; j < (int)v.size(); j++) {
      if (adjm[v[i]][v[j]] == 0) return false;
    }
  }
  return true;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, m, x, y;
  cin >> n >> m;
  for (long long int i = 0; i < (long long int)m; i++)
    cin >> x >> y, adj[x].push_back(y), adj[y].push_back(x), deg[x]++, deg[y]++,
        adjm[x][y] = adjm[y][x] = 1;
  for (long long int i = 0; i < (long long int)n; i++)
    if (deg[i + 1] == n - 1) ans[i + 1] = 'b', b.push_back(i + 1);
  for (long long int i = 0; i < (long long int)n; i++) {
    if (ans[i + 1] == '-') {
      dfs(i + 1);
      break;
    }
  }
  for (long long int i = 0; i < (long long int)n; i++) {
    if (ans[i + 1] == '-') {
      ans[i + 1] = 'c';
      c.push_back(i + 1);
    }
  }
  if (checker(a) && checker(b) && checker(c)) {
    cout << "Yes\n";
    for (long long int i = 0; i < (long long int)n; i++) cout << ans[i + 1];
  } else
    cout << "No";
  return 0;
}
