#include <bits/stdc++.h>
using namespace std;
int w[510][510], n, m, C[510];
void DFS(int a, int ck) {
  int i;
  C[a] = ck;
  for (i = 1; i <= n; i++) {
    if (!C[i] && w[a][i]) {
      DFS(i, 3 - ck);
    }
  }
}
int main() {
  int a, b, i, j, chk = 0;
  scanf("%d%d", &n, &m);
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= n; j++) {
      if (i != j) w[i][j] = 1;
    }
  }
  while (m--) {
    scanf("%d%d", &a, &b);
    w[a][b] = w[b][a] = 0;
  }
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= n; j++) {
      if (w[i][j] == 1) break;
    }
    if (j != n + 1) break;
  }
  if (i != n + 1) {
    DFS(i, 1);
    for (i = 1; i <= n; i++) {
      for (j = 1; j <= n; j++) {
        if (w[i][j] == 0 && C[i] + C[j] == 3) chk = 1;
        if (w[i][j] == 1 && C[i] + C[j] != 3) chk = 1;
      }
    }
  }
  if (chk) {
    printf("No\n");
  } else {
    printf("Yes\n");
    for (i = 1; i <= n; i++) {
      if (C[i] == 1)
        printf("a");
      else if (C[i] == 2)
        printf("c");
      else
        printf("b");
    }
  }
}
