#include <bits/stdc++.h>
using namespace std;
int n, m, dp[505][505], g[505], x, y;
char arr[503];
int main() {
  scanf("%d %d", &n, &m);
  for (int i = 1; i <= m; i++) {
    scanf("%d %d", &x, &y);
    g[x]++;
    g[y]++;
    dp[x][y] = 1;
    dp[y][x] = 1;
  }
  for (int i = 1; i <= n; i++) {
    if (g[i] == n - 1) {
      arr[i] = 'b';
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (i == j) continue;
      if (!dp[i][j]) {
        if (!arr[i] && !arr[j]) {
          arr[i] = 'a';
          arr[j] = 'c';
        } else if (!arr[i] && arr[j]) {
          arr[i] = (arr[j] == 'a' ? 'c' : 'a');
        } else if (arr[i] && !arr[j]) {
          arr[j] = (arr[i] == 'a' ? 'c' : 'a');
        } else if (arr[i] == arr[j]) {
          printf("No");
          return 0;
        }
      } else if ((arr[i] == 'a' && arr[j] == 'c') ||
                 (arr[i] == 'c' && arr[j] == 'a')) {
        printf("No");
        return 0;
      }
    }
  }
  printf("Yes\n");
  for (int i = 1; i <= n; i++) {
    printf("%c", arr[i]);
  }
  return 0;
}
