#include <bits/stdc++.h>
using namespace std;
int ar[600][600], e[600][600];
int vis[600] = {0};
int edg = 0, ver = 0;
void dfs(int u, int n, int v) {
  ver++;
  int i;
  for (i = 1; i <= n; i++) {
    if (ar[u][i] == 1 && i != u) {
      if (e[u][i] == 0) {
        e[u][i] = 1;
        e[i][u] = 1;
        edg++;
      }
      if (!vis[i]) {
        vis[i] = v;
        dfs(i, n, v);
      }
    }
  }
}
int main() {
  int n, m;
  cin >> n >> m;
  memset(e, 0, sizeof(e));
  memset(ar, 0, sizeof(ar));
  memset(vis, 0, sizeof(vis));
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    ar[a][b] = 1;
    ar[b][a] = 1;
  }
  int j = 0;
  int edges[500][3];
  for (int i = 1; i <= n; i++) {
    if (vis[i] == 0) {
      edg = 0;
      ver = 0;
      vis[i] = i;
      dfs(i, n, i);
      edges[j][0] = edg;
      edges[j][1] = i;
      edges[j][2] = ver;
      j++;
    }
  }
  if (j >= 3)
    cout << "No";
  else {
    if (j == 2) {
      if ((edges[0][2] * (edges[0][2] - 1)) / 2 == edges[0][0] &&
          (edges[1][2] * (edges[1][2] - 1)) / 2 == edges[1][0]) {
        cout << "Yes" << endl;
        for (int i = 1; i <= n; i++) {
          if (vis[i] == edges[0][1])
            cout << "a";
          else if (vis[i] == edges[1][1])
            cout << "c";
        }
      } else
        cout << "No";
    } else if (j == 1) {
      for (int i = 1; i <= n; i++) ar[i][i] = 1;
      int count[n + 1];
      memset(count, 0, sizeof(count));
      for (int i = 1; i <= n; i++) {
        for (int ji = 1; ji <= n; ji++) {
          if (ar[i][ji] == 1) {
            count[ji]++;
          }
        }
      }
      set<int> s;
      for (int i = 1; i <= n; i++) {
        s.insert(count[i]);
      }
      if (s.size() > 3) {
        cout << "No" << endl;
      } else {
        int ch[n + 1];
        int b = -1, a = -1;
        int totb = 0;
        memset(ch, -1, sizeof(ch));
        for (int i = 1; i <= n; i++) {
          if (count[i] == n) {
            ch[i] = 1;
            b = i;
            totb++;
          } else
            a = i;
        }
        int tot[3] = {0};
        if (totb == n) {
          cout << "Yes" << endl;
          for (int i = 1; i <= n; i++) cout << "b";
        } else if (totb == 0) {
          if ((edges[0][2] * (edges[0][2] - 1)) / 2 == edges[0][0])
            for (int i = 1; i <= n; i++) cout << "a";
          else
            cout << "No";
        } else {
          int ta = 0, tc = 0;
          int c = -1;
          int flag = 0;
          for (int i = 1; i <= n; i++) {
            if (count[i] == n) continue;
            if (ar[a][i] == 0) {
              tc++;
              c = i;
            } else {
              ta++;
              if (count[i] != count[a]) {
                flag = 1;
                break;
              }
            }
          }
          if (flag == 0) {
            int kl = 0;
            for (int i = 1; i <= n; i++) {
              if (count[i] == n) continue;
              if (ar[c][i] == 1) {
                kl++;
                if (count[i] != count[c]) {
                  flag = 1;
                  break;
                }
              }
            }
            if (flag == 1) {
              cout << "No";
            } else {
              if (totb + kl + ta == n) {
                cout << "Yes" << endl;
                for (int i = 1; i <= n; i++) {
                  if (ch[i] == 1) {
                    cout << "b";
                    continue;
                  }
                  if (ar[b][i] == 1 && ar[a][i] == 1)
                    cout << "a";
                  else
                    cout << "c";
                }
              } else
                cout << "No";
            }
          } else
            cout << "No";
        }
      }
    } else {
      cout << "No";
    }
  }
  return 0;
}
