#include <bits/stdc++.h>
using namespace std;
int n, m, a[505][505], l[505], u, v, ans, ok;
char s[505];
int main() {
  scanf("%d %d", &n, &m);
  for (int i = 1; i <= m; i++) {
    scanf("%d %d", &u, &v);
    a[u][v] = 1;
    a[v][u] = 1;
    l[u]++;
    l[v]++;
  }
  for (int i = 1; i <= n; i++) {
    if (l[i] == n - 1) s[i] = 'b';
  }
  int i = 1;
  while (s[i] == 'b' && i <= n) i++;
  for (int j = 1; j <= n; j++) {
    if (a[i][j] == 0)
      s[j] = 'c';
    else if (s[j] != 'b')
      s[j] = 'a';
  }
  s[i] = 'a';
  for (int i = 1; i <= n && ok != -1; i++) {
    for (int j = i + 1; j <= n; j++) {
      if (a[i][j] == 0 && (s[i] == s[j] || s[i] == 'b' || s[j] == 'b') ||
          a[i][j] == 1 &&
              ((s[i] == 'a' && s[j] == 'c') || (s[i] == 'c' && s[j] == 'a')))
        ok = -1;
    }
  }
  if (ok == -1) {
    printf("No\n");
  } else {
    printf("Yes\n");
    for (int i = 1; i <= n; i++) printf("%c", s[i]);
    printf("\n");
  }
  return 0;
}
