#include <bits/stdc++.h>
using namespace std;
void __print(long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
template <typename T, typename V>
void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T>
void __print(const T &x) {
  long long f = 0;
  cerr << '{';
  for (auto &i : x) cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V>
void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v)) cerr << ", ";
  _print(v...);
}
const long long inf = 1e18;
const long long N = 505;
vector<long long> g[N];
long long done[N];
char color[N];
long long mat[N][N];
long long want[N][N];
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  for (long long x = 0; x < N; x++) {
    color[x] = 'z';
  }
  long long n, m;
  cin >> n >> m;
  for (long long x = 0; x < m; x++) {
    long long u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  for (long long x = 1; x <= n; x++) {
    if (g[x].size() == (n - 1)) {
      done[x] = 1;
      color[x] = 'b';
    }
  }
  for (long long x = 1; x <= n; x++) {
    if (!done[x]) {
      done[x] = 1;
      color[x] = 'a';
      for (auto it : g[x]) {
        if (!done[it]) color[it] = 'a', done[it] = 1;
      }
      break;
    }
  }
  for (long long x = 1; x <= n; x++) {
    if (!done[x]) color[x] = 'c';
  }
  for (long long x = 1; x <= n; x++) {
    for (auto y : g[x]) {
      mat[x][y] = 1;
    }
  }
  for (long long x = 1; x <= n; x++) {
    for (long long y = 1; y <= n; y++) {
      if (abs(color[x] - color[y]) <= 1 and (x != y))
        want[x][y] = 1, want[y][x] = 1;
    }
  }
  for (long long x = 1; x <= n; x++) {
    for (long long y = 1; y <= (n); y++) {
      if (want[x][y] != mat[x][y]) {
        cout << "No\n";
        return 0;
      }
    }
  }
  cout << "Yes" << '\n';
  for (long long x = 1; x <= n; x++) cout << color[x];
  cout << '\n';
  return 0;
}
