#include <bits/stdc++.h>
using namespace std;
int INT_MAX_VAL = (int)0x3F3F3F3F;
int INT_MIN_VAL = (int)-0x3F3F3F3F;
long long LONG_MAX_VAL = (long long)0x3F3F3F3F3F3F3F3F;
long long LONG_MIN_VAL = (long long)-0x3F3F3F3F3F3F3F3F;
int G[505][505];
int deg[505];
int color[505];
int n;
int dfs(int v) {
  for (long long(w) = 0LL; (w) < (n); (w)++) {
    if (G[v][w]) {
      if (color[w] == 0) {
        color[w] = 3 - color[v];
        if (dfs(w) == -1) return -1;
      } else if (color[v] == color[w]) {
        return -1;
      }
    }
  }
  return 1;
}
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int m;
  cin >> n >> m;
  for (long long(i) = 0LL; (i) < (m); (i)++) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    G[a][b] = 1;
    G[b][a] = 1;
    deg[a]++;
    deg[b]++;
  }
  for (long long(i) = 0LL; (i) < (n); (i)++)
    for (long long(j) = 0LL; (j) < (n); (j)++)
      if (i != j) G[i][j] = 1 - G[i][j];
  for (long long(i) = 0LL; (i) < (n); (i)++) G[i][i] = 0;
  for (long long(i) = 0LL; (i) < (n); (i)++) {
    if (color[i] == 0) {
      color[i] = 1;
      if (dfs(i) == -1) {
        cout << "No" << '\n';
        return 0;
      }
    }
  }
  string ans(n, '0');
  for (long long(i) = 0LL; (i) < (n); (i)++) {
    if (deg[i] == n - 1) {
      ans[i] = 'b';
    } else if (color[i] == 1) {
      ans[i] = 'a';
    } else if (color[i] == 2) {
      ans[i] = 'c';
    }
  }
  for (long long(i) = 0LL; (i) < (n); (i)++)
    for (long long(j) = 0LL; (j) < (n); (j)++)
      if (i != j) {
        if ((ans[i] == 'a' && ans[j] == 'c') ||
            (ans[i] == 'c' && ans[j] == 'a')) {
          if (!G[i][j]) {
            cout << "No" << '\n';
            return 0;
          }
        } else if (G[i][j]) {
          cout << "No" << '\n';
          return 0;
        }
      }
  cout << "Yes" << '\n';
  cout << ans << '\n';
  return 0;
}
