#include <bits/stdc++.h>
using namespace std;
int n, m, i, j, x, y, a[505][505], s[505];
int main() {
  cin >> n >> m;
  for (i = 1; i <= m; ++i) {
    cin >> x >> y;
    a[x][y] = 1;
    a[y][x] = 1;
  }
  for (i = 1; i <= n; ++i) {
    for (j = 1; j <= n; ++j)
      if (i != j && a[i][j] == 0) {
        if (s[i] != 0) {
          if (s[i] == s[j]) {
            cout << "No";
            return 0;
          }
          if (s[i] == 1)
            s[j] = 2;
          else
            s[j] = 1;
          continue;
        }
        s[i] = 1;
        s[j] = 2;
      }
  }
  for (i = 1; i <= n; ++i)
    for (j = 1; j <= n; ++j)
      if (a[i][j] != 0 && s[i] + s[j] == 3) {
        cout << "No";
        return 0;
      }
  cout << "Yes\n";
  for (i = 1; i <= n; ++i)
    if (s[i] == 1)
      cout << "a";
    else if (s[i] == 2)
      cout << "c";
    else
      cout << "b";
}
