#include <bits/stdc++.h>
using namespace std;
bool graph[500][500];
char s[501];
int main() {
  int n, m;
  cin >> n >> m;
  if (m == (n * (n - 1)) / 2) {
    for (int i = 0; i < n; i++) {
      s[i] = 'b';
    }
    cout << "Yes" << endl;
    cout << s << endl;
    return 0;
  }
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    graph[u - 1][v - 1] = true;
    graph[v - 1][u - 1] = true;
  }
  bool found = false;
  int a, c;
  for (int row = 0; row < n; row++) {
    for (int col = 0; col < n; col++) {
      if (row == col) {
        continue;
      }
      if (!graph[row][col]) {
        a = row;
        c = col;
        found = true;
        break;
      }
    }
    if (found) {
      break;
    }
  }
  s[a] = 'a';
  s[c] = 'c';
  bool valid = true;
  for (int i = 0; i < n; i++) {
    if (i == a || i == c) {
      continue;
    }
    if (graph[i][a] && graph[i][c]) {
      s[i] = 'b';
    } else if (graph[i][a]) {
      s[i] = 'a';
    } else if (graph[i][c]) {
      s[i] = 'c';
    } else {
      valid = false;
      break;
    }
  }
  for (int i = 0; i < n && valid; i++) {
    if (s[i] == 'b') {
      for (int j = 0; j < n; j++) {
        if (j == i) {
          continue;
        }
        if (!graph[i][j]) {
          valid = false;
          break;
        }
      }
    } else {
      for (int j = 0; j < n; j++) {
        if (j == i) {
          continue;
        }
        if (s[j] == s[i] || s[j] == 'b') {
          if (!graph[i][j]) {
            valid = false;
            break;
          }
        } else {
          if (graph[i][j]) {
            valid = false;
            break;
          }
        }
      }
    }
  }
  if (valid) {
    cout << "Yes" << endl;
    cout << s << endl;
  } else {
    cout << "No" << endl;
  }
  return 0;
}
