#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
long long int C(int n, int k) {
  long long ans = 1;
  k = k > n - k ? n - k : k;
  int j = 1;
  for (; j <= k; j++, n--) {
    if (n % j == 0) {
      ans *= n / j;
    } else if (ans % j == 0) {
      ans = ans / j * n;
    } else {
      ans = (ans * n) / j;
    }
  }
  return ans;
}
long long int powmod(long long int a, long long int b) {
  long long int res = 1;
  a %= mod;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
long long int gcd(long long int a, long long int b) {
  if (a == 0)
    return (b);
  else
    return (gcd(b % a, a));
}
long long int powmod(long long int a, long long int b, long long int m) {
  long long int res = 1;
  a %= m;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % m;
    a = a * a % m;
  }
  return res;
}
int countSetBits(long long int n) {
  unsigned int count = 0;
  while (n) {
    n &= (n - 1);
    count++;
  }
  return count;
}
int members[100010];
int a[100010];
set<pair<int, int> > sets;
void init(int n) {
  for (int i = 0; i <= n; i++) {
    a[i] = i;
    members[i] = 1;
    sets.insert(pair<int, int>(1, i));
  }
}
int rootof(int x) {
  if (a[x] != x) {
    a[x] = rootof(a[x]);
  }
  return a[x];
}
void unite(int x, int y) {
  x = rootof(x);
  y = rootof(y);
  if (x != y) {
    if (members[x] < members[y]) {
      swap(x, y);
    }
    a[y] = x;
    sets.erase(pair<int, int>(members[x], x));
    sets.erase(pair<int, int>(members[y], y));
    members[x] += members[y];
    sets.insert(pair<int, int>(members[x], x));
  }
}
int main() {
  std::ios::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  vector<vector<int> > graph(n);
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    x--, y--;
    graph[x].push_back(y);
    graph[y].push_back(x);
  }
  string ans = "";
  for (int i = 0; i < n; i++) {
    ans += " ";
  }
  int count = 0;
  for (int i = 0; i < n; i++) {
    sort((graph[i]).begin(), (graph[i]).end());
    if (graph[i].size() == n - 1) {
      ans[i] = 'b';
      count++;
    }
  }
  if (count == n) {
    cout << "Yes" << '\n';
    cout << ans << '\n';
    return 0;
  }
  string temp = ans;
  bool flag = false;
  for (int i = 0; i < n; i++) {
    if (ans[i] == ' ') {
      ans[i] = 'a';
      count++;
      for (int j = 0; j < graph[i].size(); j++) {
        if (ans[graph[i][j]] == ' ') {
          ans[graph[i][j]] = 'a';
          count++;
        }
      }
      break;
    }
  }
  for (int i = 0; i < n; i++) {
    if (ans[i] == ' ') {
      ans[i] = 'c';
      count++;
      for (int j = 0; j < graph[i].size(); j++) {
        if (ans[graph[i][j]] == ' ') {
          ans[graph[i][j]] = 'c';
          count++;
        }
      }
      break;
    }
  }
  vector<vector<int> > test(n);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (j != i and (ans[j] == ans[i] or abs(ans[j] - ans[i]) == 1)) {
        test[i].push_back(j);
      }
    }
    sort((test[i]).begin(), (test[i]).end());
  }
  if (test != graph or count != n) {
    cout << "No" << '\n';
  } else {
    cout << "Yes" << '\n';
    cout << ans << '\n';
  }
  return 0;
}
