#include <bits/stdc++.h>
using namespace std;
int n, m;
int a[555][555];
char ans[555];
void die() {
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      if (i != j) {
        if (abs(ans[i] - ans[j]) <= 1 && !a[i][j]) {
          cout << "No\n";
          exit(0);
        }
        if (abs(ans[i] - ans[j]) > 1 && a[i][j]) {
          cout << "No\n";
          exit(0);
        }
      }
    }
  }
  cout << "Yes\n";
  ans[n] = 0;
  cout << ans << endl;
  exit(0);
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < m; ++i) {
    int first, second;
    scanf("%d%d", &first, &second);
    --first;
    --second;
    a[first][second] = a[second][first] = 1;
  }
  int A = -1, B = -1, C = -1;
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      for (int k = 0; k < n; ++k) {
        if (i == j || j == k) {
          continue;
        }
        if (a[i][j] && a[i][k]) {
          if (!a[j][k]) {
            A = j;
            B = i;
            C = k;
          }
        }
      }
    }
  }
  if (A == -1) {
    ans[0] = 'a';
    for (int i = 1; i < n; ++i) {
      if (a[0][i]) {
        ans[i] = 'a';
      } else {
        ans[i] = 'c';
      }
    }
    die();
  }
  ans[B] = 'b';
  ans[A] = 'a';
  ans[C] = 'c';
  for (int i = 0; i < n; ++i) {
    if (i == A || i == B || i == C) continue;
    if (a[A][i] && a[B][i] && a[C][i])
      ans[i] = 'b';
    else if (a[A][i] && a[B][i])
      ans[i] = 'a';
    else
      ans[i] = 'c';
  }
  die();
}
