#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 505;
vector<int> e[MAX_N];
char s[MAX_N];
int sm[MAX_N][MAX_N];
void dfs(int v) {
  s[v] = 'a';
  for (int i = 0; i < (int)e[v].size(); i++)
    if (s[e[v][i]] == 'c') dfs(e[v][i]);
}
int main() {
  int n, m;
  scanf("%d %d", &n, &m);
  if (n > 2 && m == 0) {
    cout << "No";
    return 0;
  }
  for (int i = 0; i < m; i++) {
    int x, y;
    scanf("%d %d", &x, &y);
    x--;
    y--;
    e[x].push_back(y);
    e[y].push_back(x);
    sm[x][y] = sm[y][x] = 1;
  }
  for (int i = 0; i < n; i++) s[i] = 'c';
  for (int i = 0; i < n; i++)
    if ((int)e[i].size() == n - 1) s[i] = 'b';
  for (int i = 0; i < n; i++)
    if ((int)e[i].size() < n - 1) {
      dfs(i);
      break;
    }
  for (int i = 0; i < n; i++)
    if (s[i] != 'b') {
      for (int j = 0; j < (int)e[i].size(); j++) {
        int new_v = e[i][j];
        if (!(s[new_v] == 'b' || s[new_v] == s[i])) {
          cout << "No";
          return 0;
        }
      }
    }
  for (int i = 0; i < n; i++)
    for (int j = i + 1; j < n; j++)
      if ((s[i] == s[j] || s[i] == 'b' || s[j] == 'b') && sm[i][j] == 0) {
        cout << "No";
        return 0;
      }
  cout << "Yes\n";
  for (int i = 0; i < n; i++) cout << s[i];
  return 0;
}
