#include <bits/stdc++.h>
using namespace std;
bool graph[500][500];
int main() {
  int n, m;
  cin >> n >> m;
  memset(graph, false, sizeof(graph));
  for (int i = 0; i < n; i++) graph[i][i] = 1;
  char word[n];
  for (int i = 0; i < n; i++) word[i] = 'd';
  for (int i = 0; i < m; i++) {
    int s, d;
    cin >> s >> d;
    s--;
    d--;
    graph[s][d] = true;
    graph[d][s] = true;
  }
  for (int i = 0; i < n; i++) {
    int count = 0;
    for (int j = 0; j < n; j++) count += graph[i][j];
    if (count == n) {
      word[i] = 'b';
      continue;
    }
    bool ag = false, cg = false, ang = false, cng = false;
    for (int j = 0; j < n; j++) {
      if (word[j] == 'a' && graph[i][j]) ag = true;
      if (word[j] == 'c' && graph[i][j]) cg = true;
      if ((!graph[i][j]) && (word[j] == 'b' || word[j] == 'a')) ang = true;
      if ((!graph[i][j]) && (word[j] == 'b' || word[j] == 'c')) cng = true;
    }
    if (ang && cng || (ag && ang) || (cg && cng)) {
      cout << "No";
      return 0;
    }
    if ((ag && !ang) || !(ag || ang))
      word[i] = 'a';
    else if ((cg && !cng) || !(cg || cng))
      word[i] = 'c';
    else {
      cout << "No";
      return 0;
    }
  }
  cout << "Yes\n";
  for (int i = 0; i < n; i++) cout << word[i];
}
