#include <bits/stdc++.h>
using namespace std;
int n, m, g[501][501];
char ans[501], f[501];
int main() {
  ios_base::sync_with_stdio(false);
  cout.tie(0);
  cin.tie(0);
  cin >> n >> m;
  for (int i = 0, u, v; i < m; i++) {
    cin >> u >> v;
    g[u][v] = g[v][u] = 1;
  }
  for (int i = 1; i <= n; i++) {
    if (!ans[i]) {
      ans[i] = 'a';
    }
    for (int j = i + 1; j <= n; j++) {
      if (!g[i][j]) {
        f[i] = f[j] = 1;
        if (ans[i] == ans[j]) {
          cout << "No"
               << "\n";
          return 0;
        }
        ans[j] = ans[i] == 'a' ? 'c' : 'a';
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    if (!ans[i]) {
      ans[i] = 'a';
    }
    for (int j = i + 1; j <= n; j++) {
      if (g[i][j]) {
        if (abs(ans[i] - ans[j]) > 1) {
          if (f[i] && f[j]) {
            cout << "No"
                 << "\n";
            return 0;
          }
          if (f[i]) {
            f[j] = 1;
            ans[j] = 'b';
          } else {
            f[i] = 1;
            ans[i] = 'b';
          }
        }
      }
    }
  }
  cout << "Yes"
       << "\n";
  for (int i = 1; i <= n; i++) {
    cout << ans[i];
  }
  return 0;
}
