#include <bits/stdc++.h>
using namespace std;
int cnt[555];
bool edge[555][555];
char ans[555];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; ++i) {
    int x, y;
    cin >> x >> y;
    --x, --y;
    edge[x][y] = edge[y][x] = 1;
    cnt[x]++;
    cnt[y]++;
  }
  for (int i = 0; i < n; ++i) {
    if (cnt[i] == n - 1) ans[i] = 'b';
  }
  for (int i = 0; i < n; ++i) {
    if (!ans[i]) {
      ans[i] = 'a';
      for (int j = 0; j < n; ++j) {
        if (!ans[j]) {
          if (edge[i][j])
            ans[j] = 'a';
          else
            ans[j] = 'c';
        }
      }
    }
  }
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      if (i == j) continue;
      if ((abs(ans[i] - ans[j]) == 2 && edge[i][j]) ||
          (abs(ans[i] - ans[j]) < 2 && !edge[i][j])) {
        cout << "No";
        return 0;
      }
    }
  }
  cout << "Yes\n" << ans << endl;
  return 0;
}
