#include <bits/stdc++.h>
using namespace std;
bool e[501][501] = {};
char s[501] = {};
bool vis[501] = {};
int n, m;
int u, v;
bool bj;
bool fail;
int main() {
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    cin >> u >> v;
    e[u][v] = 1;
    e[v][u] = 1;
  }
  bj = 1;
  while (fail == 0 && bj == 1) {
    bj = 0;
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= n; j++) {
        if (i != j && e[i][j] == 0) {
          if (vis[i] == vis[j]) {
            if (vis[i] == 0) {
              bj = 1;
              vis[i] = 1;
              vis[j] = 1;
              s[i] = 'a';
              s[j] = 'c';
            } else {
              if (s[i] == s[j]) {
                fail = 1;
                break;
              }
            }
          } else {
            if (vis[i] == 0) {
              bj = 1;
              vis[i] = 1;
              if (s[j] == 'c')
                s[i] = 'a';
              else
                s[i] = 'c';
            } else {
              bj = 1;
              vis[j] = 1;
              if (s[i] == 'c')
                s[j] = 'a';
              else
                s[j] = 'c';
            }
          }
        }
        if (e[i][j] == 1) {
          if (vis[i] == vis[j] && vis[i] == 1) {
            if (s[i] != s[j]) {
              fail = 1;
              break;
            }
          }
        }
      }
    }
  }
  if (fail == 1) {
    cout << "No";
  } else {
    cout << "Yes" << endl;
    for (int i = 1; i <= n; i++) {
      if (s[i] == 0) s[i] = 'b';
      cout << s[i];
    }
  }
  return 0;
}
