#include <bits/stdc++.h>
using namespace std;
const int N = 1000;
bool was[N][N];
int type[N];
vector<int> a[N];
set<int> s;
int main() {
  srand(time(NULL));
  int n, m;
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    int x, y;
    cin >> x >> y;
    a[x].push_back(y);
    a[y].push_back(x);
    was[x][y] = true;
    was[y][x] = true;
  }
  int kol = 0;
  for (int i = 1; i <= n; i++) {
    if (a[i].size() == n - 1) {
      type[i] = 1;
      kol++;
    }
  }
  int cnt = 1;
  for (int i = 1; i <= n; i++) {
    if (type[i] == 1) continue;
    if (type[i] == 0) {
      cnt++;
      type[i] = cnt;
    }
    for (int j = i + 1; j <= n; j++) {
      if (type[j] == 1) continue;
      if (!was[i][j]) continue;
      if (type[j] == 0) {
        type[j] = type[i];
        continue;
      }
      if (type[i] != type[j]) cout << "No", exit(0);
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (type[i] == type[j] && !was[i][j]) {
        cerr << i << " " << j << endl;
        cout << "No", exit(0);
      }
    }
  }
  if (cnt > 3) {
    cout << "No", exit(0);
  }
  cout << "Yes\n";
  for (int i = 1; i <= n; i++) {
    if (type[i] == 1) {
      cout << "b";
    } else {
      if (type[i] == 2) {
        cout << "a";
      } else {
        cout << "c";
      }
    }
  }
  return 0;
}
