#include <bits/stdc++.h>
using namespace std;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
int g[505][505];
int ie[505][505];
int ct[505], vis[505];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    g[i][i] = 1;
    ct[i]++;
    ie[i][i] = 1;
  }
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    g[u][v] = 1;
    g[v][u] = 1;
    ct[u]++;
    ct[v]++;
  }
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
      int fl = 0;
      for (int k = 0; k < n; k++) {
        if (g[i][k] != g[j][k]) fl = 1;
      }
      if (fl == 0) {
        ie[i][j] = 1;
        ie[j][i] = 1;
      }
    }
  }
  for (int i = 0; i < n; i++)
    if (ct[i] == n) vis[i] = 1;
  int comp = 1;
  for (int i = 0; i < n; i++) {
    if (vis[i] == 0) {
      comp++;
      for (int j = 0; j < n; j++) {
        if (ie[i][j]) vis[j] = comp;
      }
    }
  }
  if (comp <= 3) {
    cout << "Yes\n";
    for (int i = 0; i < n; i++) {
      if (vis[i] == 1)
        cout << 'b';
      else if (vis[i] == 2)
        cout << 'c';
      else
        cout << 'a';
    }
    cout << "\n";
  } else
    cout << "No\n";
  return 0;
}
