#include <bits/stdc++.h>
using namespace std;
const long long INF = (long long)1e9 + 37;
const double PI = acos(-1.0);
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
bool ok = 1;
bool used[555];
int type[555];
void build(vector<vector<int> >& a, int v) {
  type[v] = 1;
  for (int i = 0; i < (int)a[v].size(); i++) {
    if (type[a[v][i]] == 0) {
      build(a, a[v][i]);
    }
  }
}
void checkA(vector<int>& as, vector<vector<int> >& a) {
  int sz = (int)as.size();
  for (int i = 0; i < sz - 1; i++) {
    for (int j = i + 1; j < sz; j++) {
      bool edgeFound = 0;
      for (int it = 0; it < (int)a[as[i]].size(); it++) {
        if (a[as[i]][it] == as[j]) {
          edgeFound = 1;
          break;
        }
      }
      if (!edgeFound) {
        ok = 0;
      }
    }
  }
}
void checkC(vector<int>& cs, vector<vector<int> >& a) {
  int sz = (int)cs.size();
  for (int i = 0; i < sz - 1; i++) {
    for (int j = i + 1; j < sz; j++) {
      bool edgeFound = 0;
      for (int it = 0; it < (int)a[cs[i]].size(); it++) {
        if (a[cs[i]][it] == cs[j]) {
          edgeFound = 1;
          break;
        }
      }
      if (!edgeFound) {
        ok = 0;
      }
    }
  }
}
void printVector(vector<int>& tmp) {
  for (int i = 0; i < (int)tmp.size(); i++) {
    printf("%d ", tmp[i]);
  }
  cout << endl;
}
int main() {
  int n, m, x, y;
  cin >> n >> m;
  vector<vector<int> > a(n);
  vector<int> as, cs;
  for (int i = 0; i < m; i++) {
    scanf("%d%d", &x, &y);
    x--, y--;
    a[x].push_back(y);
    a[y].push_back(x);
  }
  for (int i = 0; i < n; i++) {
    if ((int)a[i].size() == n - 1) {
      type[i] = 2;
    }
  }
  for (int i = 0; i < n; i++) {
    if (type[i] == 0) {
      build(a, i);
      break;
    }
  }
  for (int i = 0; i < n; i++) {
    if (type[i] == 0) {
      type[i] = 3;
    }
  }
  for (int i = 0; i < n; i++) {
    if (type[i] == 1) {
      as.push_back(i);
    }
    if (type[i] == 3) {
      cs.push_back(i);
    }
  }
  checkA(as, a);
  checkC(cs, a);
  if (!ok) {
    printf("No\n");
    return 0;
  } else {
    printf("Yes\n");
    for (int i = 0; i < n; i++) {
      cout << char(type[i] + 'a' - 1);
    }
  }
  return 0;
}
