#include <bits/stdc++.h>
using namespace std;
const long long N = (long long)5e3 + 113;
const long long Dec = (long long)1e4;
int n, m, last_col, a, c;
pair<int, int> Rebr, Ver;
int col[N], dp[N][N];
vector<int> gr[N], no_gr[N];
vector<pair<int, int> > rebr;
void dfs(int v, int typ) {
  col[v] = typ;
  for (int i = 0; i < (int)gr[v].size(); i++) {
    int to = gr[v][i];
    if (!col[to]) dfs(to, typ);
  }
}
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    gr[u].push_back(v);
    gr[v].push_back(u);
    dp[u][v] = dp[v][u] = 1;
    rebr.push_back(make_pair(v, u));
  }
  for (int i = 1; i <= n; i++) {
    if (!col[i]) {
      last_col++;
      dfs(i, last_col);
    }
  }
  if (last_col > 2) {
    cout << "NO";
    return 0;
  }
  if (last_col == 2) {
    for (int i = 0; i < m; i++) {
      if (col[rebr[i].first] == 1) {
        Rebr.first++;
      } else {
        Rebr.second++;
      }
    }
    for (int i = 1; i <= n; i++) {
      if (col[i] == 1) {
        Ver.first++;
      } else {
        Ver.second++;
      }
    }
    if ((Ver.first * (Ver.first - 1) / 2 != Rebr.first) ||
        (Ver.second * (Ver.second - 1) / 2 != Rebr.second)) {
      cout << "No";
      return 0;
    }
    string ans = "";
    for (int i = 1; i <= n; i++) {
      if (col[i] == 1) {
        ans += "a";
      } else {
        ans += "c";
      }
    }
    cout << "Yes" << endl;
    cout << ans;
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (!dp[i][j]) {
        no_gr[i].push_back(j);
        no_gr[j].push_back(i);
        a = i;
        c = j;
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    col[i] = 2;
  }
  for (int i = 0; i < no_gr[c].size(); i++) {
    col[no_gr[c][i]] = 1;
  }
  for (int i = 0; i < (int)no_gr[a].size(); i++) {
    col[no_gr[a][i]] = 3;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (abs(col[i] - col[j]) <= 1) {
        if (!dp[i][j]) {
          cout << "No";
          return 0;
        }
      } else {
        if (dp[i][j]) {
          cout << "No";
          return 0;
        }
      }
    }
  }
  string ans = "";
  for (int i = 1; i <= n; i++) {
    if (col[i] == 1) ans += 'a';
    if (col[i] == 2) ans += 'b';
    if (col[i] == 3) ans += 'c';
  }
  cout << "Yes" << endl;
  cout << ans;
  return 0;
}
