#include <bits/stdc++.h>
using namespace std;
const int N = 510;
int n, m;
int flag;
int a[N][N];
int c[N];
void dfs(int i) {
  for (int j = 1; j <= n; j++)
    if (a[i][j]) {
      if (c[j] == -1) {
        c[j] = 2 - c[i];
        dfs(j);
      } else if (c[i] + c[j] != 2)
        flag = 1;
    } else {
      if (c[j] == -1) {
        c[j] = c[i];
        dfs(j);
      } else if (c[j] + c[i] == 2)
        flag = 1;
    }
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= m; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    a[x][y] = a[y][x] = 1;
  }
  for (int i = 1; i <= n; i++) a[i][i] = 1;
  for (int i = 1; i <= n; i++) c[i] = -1;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) a[i][j] ^= 1;
  for (int i = 1; i <= n; i++) {
    int cnt = 0;
    for (int j = 1; j <= n; j++) cnt += a[i][j];
    if (cnt == 0) c[i] = 1;
  }
  flag = 0;
  for (int i = 1; i <= n; i++)
    if (c[i] == -1) {
      c[i] = 0;
      dfs(i);
    }
  if (flag)
    printf("No\n");
  else {
    printf("Yes\n");
    for (int i = 1; i <= n; i++) printf("%c", c[i] + 97);
  }
  return 0;
}
