#include <bits/stdc++.h>
using namespace std;
int a[505];
vector<int> edge[505];
void bfs(int u, int k) {
  queue<int> q;
  q.push(u);
  a[u] = k;
  while (!q.empty()) {
    int x = q.front();
    q.pop();
    for (auto v : edge[x]) {
      if (a[v]) continue;
      a[v] = k;
      q.push(v);
    }
  }
}
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    int u, v;
    cin >> u >> v;
    edge[u].push_back(v);
    edge[v].push_back(u);
  }
  for (int i = 1; i <= n; i++) {
    if (edge[i].size() > n - 1) {
      cout << "No" << endl;
      return 0;
    }
    if (edge[i].size() == n - 1) a[i] = 3;
  }
  int now = 1, num1 = 0, num2 = 0;
  for (int i = 1; i <= n; i++) {
    if (now == 3) break;
    if (!a[i]) bfs(i, now++);
  }
  for (int i = 1; i <= n; i++) {
    if (!a[i]) {
      cout << "No" << endl;
      return 0;
    }
    if (a[i] == 1) num1++;
    if (a[i] == 2) num2++;
  }
  for (int i = 1; i <= n; i++) {
    if (a[i] == 1) {
      if (edge[i].size() != n - num2 - 1) {
        cout << "No" << endl;
        return 0;
      }
    }
    if (a[i] == 2) {
      if (edge[i].size() != n - num1 - 1) {
        cout << "No" << endl;
        return 0;
      }
    }
  }
  cout << "Yes" << endl;
  for (int i = 1; i <= n; i++) {
    if (a[i] == 1) cout << 'a';
    if (a[i] == 2) cout << 'c';
    if (a[i] == 3) cout << 'b';
  }
  cout << endl;
}
