#include <bits/stdc++.h>
using namespace std;
int n, m;
const int mx = 505;
bool conn[mx][mx];
string s;
void eval(int i, char c) {
  s[i] = c;
  for (int j = 0; j < n; j++)
    if (i != j)
      if (!conn[i][j] && s[j] == 'b')
        eval(j, 'a' + 'c' - c);
      else if (conn[i][j] && s[j] != 'b' && s[j] != s[i] ||
               !conn[i][j] && s[i] == s[j]) {
        cout << "No" << endl;
        exit(0);
      }
}
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    conn[a][b] = conn[b][a] = true;
  }
  s = string(n, 'b');
  for (int i = 0; i < n; i++)
    if (s[i] == 'b')
      for (int j = i + 1; j < n; j++)
        if (!conn[i][j]) eval(i, 'a');
  cout << "Yes" << endl;
  cout << s << endl;
  return 0;
}
