#include <bits/stdc++.h>
const int ms = 500;
std::vector<int> edges[ms], check[ms];
char a[ms];
int main() {
  int n, m;
  std::cin >> n >> m;
  while (m--) {
    int u, v;
    std::cin >> u >> v;
    u--;
    v--;
    edges[u].push_back(v);
    edges[v].push_back(u);
  }
  int got = -1;
  for (int i = 0; i < n; i++) {
    edges[i].push_back(i);
    std::sort(edges[i].begin(), edges[i].end());
    if (edges[i].size() == n) {
      a[i] = 'b';
      continue;
    }
    if (got == -1) {
      got = i;
    }
    if (edges[i] == edges[got]) {
      a[i] = 'a';
    } else {
      a[i] = 'c';
    }
  }
  bool valid = true;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (a[i] - a[j] == 0 || a[i] - a[j] == 1 || a[i] - a[j] == -1) {
        check[i].push_back(j);
      }
    }
    valid = valid && check[i] == edges[i];
  }
  if (valid) {
    std::cout << "Yes\n";
    for (int i = 0; i < n; i++) {
      std::cout << a[i];
    }
    std::cout << '\n';
  } else {
    std::cout << "No\n";
  }
}
