#include <bits/stdc++.h>
using namespace std;
void dfs(vector<int> v[], int node, vector<int> &color, int now) {
  color[node] = now;
  for (int i = 0; i < v[node].size(); ++i) {
    int child = v[node][i];
    if (color[child]) continue;
    dfs(v, child, color, now);
  }
}
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> v[n];
  for (int i = 0; i < m; ++i) {
    int x, y;
    cin >> x >> y;
    v[x - 1].push_back(y - 1);
    v[y - 1].push_back(x - 1);
  }
  vector<int> color(n, 0);
  for (int i = 0; i < n; ++i) {
    if (v[i].size() == n - 1) {
      color[i] = 2;
    }
  }
  int now = 1;
  for (int i = 0; i < n; ++i) {
    if (color[i]) continue;
    if (now >= 5) {
      cout << "No";
      return 0;
    }
    dfs(v, i, color, now);
    now += 2;
  }
  int a = 0, b = 0, c = 0;
  for (int i = 0; i < n; ++i) {
    if (color[i] == 1)
      ++a;
    else if (color[i] == 2)
      ++b;
    else
      ++c;
  }
  for (int i = 0; i < n; ++i) {
    if (color[i] == 1) {
      if (v[i].size() != b + a - 1) {
        cout << "No";
        return 0;
      }
    } else if (color[i] == 3) {
      if (v[i].size() != b + c - 1) {
        cout << "No";
        return 0;
      }
    } else {
      if (v[i].size() != a + b + c - 1) {
        cout << "No";
        return 0;
      }
    }
  }
  cout << "Yes\n";
  for (auto x : color) cout << ((char)('a' + x - 1));
}
