#include <bits/stdc++.h>
using namespace std;
int g[555][555], ng[555][555];
int col[555];
bool vis[555];
int flag = 0;
void dfs(int n, int s, int c) {
  int i;
  vis[s] = true;
  col[s] = c;
  for (i = 1; i <= n; i++) {
    if (ng[s][i] == 1 && vis[i] == false) {
      dfs(n, i, 1 ^ c);
    } else if (ng[s][i] == 1) {
      if (col[i] != (c ^ 1)) {
        flag = 1;
      }
    }
  }
}
int main() {
  int n, m;
  cin >> n >> m;
  int i, j, u, v;
  for (i = 1; i <= m; i++) {
    cin >> u >> v;
    g[u][v] = 1;
    g[v][u] = 1;
  }
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= n; j++) {
      if (i != j) ng[i][j] = g[i][j] ^ 1;
    }
  }
  for (i = 1; i <= n; i++) {
    col[i] = -1;
  }
  for (i = 1; i <= n; i++) {
    int ff = 0;
    for (j = 1; j <= n; j++) {
      if (ng[i][j] == 1) {
        ff = 1;
        break;
      }
    }
    if (ff == 0) continue;
    if (!vis[i]) {
      dfs(n, i, 0);
    }
  }
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= n; j++) {
      if (g[i][j] == 1) {
        if (col[i] == -1 || col[j] == -1) continue;
        if (col[i] ^ col[j] == 1) {
          flag = 1;
          goto next;
        }
      }
    }
  }
next:
  if (flag == 1) {
    cout << "No\n";
    return 0;
  }
  cout << "Yes\n";
  for (i = 1; i <= n; i++) {
    if (col[i] == 0) {
      cout << "a";
    } else if (col[i] == 1) {
      cout << "c";
    } else {
      cout << "b";
    }
  }
  cout << endl;
  return 0;
}
