#include <bits/stdc++.h>
using graph = std::vector<std::set<int>>;
int main(int argc, const char *argv[]) {
  int n, m;
  std::cin >> n >> m;
  std::vector<char> string(n, '\0');
  graph g(n);
  for (int i = 0; i != n; ++i) {
    g[i].insert(i);
  }
  for (int i = 0; i != m; ++i) {
    int x, y;
    std::cin >> x >> y;
    --x;
    --y;
    g[x].insert(y);
    g[y].insert(x);
  }
  for (int i = 0; i != n; ++i) {
    if (g[i].size() == n) {
      string[i] = 'b';
    }
  }
  int i = 0;
  while (i < n && g[i].size() == n) ++i;
  if (i == n) {
    std::cout << "Yes" << std::endl;
    for (char c : string) std::cout << c;
    std::cout << std::endl;
    return 0;
  }
  string[i] = 'a';
  for (int j = 0; j != n; ++j) {
    for (int k = 0; k != n; ++k) {
      if (string[k] == '\0') {
        if (g[i].find(k) == g[i].end())
          string[k] = 'c';
        else
          string[k] = 'a';
      }
    }
  }
  graph g1(n);
  for (int i = 0; i != n; ++i) {
    for (int j = i; j != n; ++j) {
      int a = string[i], b = string[j];
      if (std::abs(a - b) <= 1) {
        g1[i].insert(j);
        g1[j].insert(i);
      }
    }
  }
  if (g == g1) {
    std::cout << "Yes" << std::endl;
    for (char c : string) std::cout << c;
    std::cout << std::endl;
    return 0;
  }
  std::cout << "No" << std::endl;
  return 0;
}
