#include <bits/stdc++.h>
using namespace std;
const long long int M = 1e3 + 7;
map<long long int, long long int> value, visit;
long long int n, m, points[M][M];
long long int bfs(long long int node) {
  long long int i;
  for (i = 1; i < n + 1; i++) {
    if (points[node][i] == 1) {
      if (value[i] == 0) {
        value[i] = value[node];
      } else if (value[i] != 2 && value[i] != value[node])
        return -1;
    }
  }
  return 0;
}
long long int check() {
  long long int i, j;
  for (i = 1; i < n + 1; i++) {
    for (j = 1; j < n + 1; j++) {
      if (points[i][j] == 1) {
        if ((value[i] == 1 && value[j] == 3) ||
            (value[i] == 3 && value[j] == 1)) {
          return 0;
        }
      }
    }
  }
}
int main() {
  scanf("%lld", &n);
  scanf("%lld", &m);
  long long int i, j, a, b, cnta = 0, cntb = 0, cntc = 0;
  for (i = 0; i < m; i++) {
    scanf("%lld", &a);
    scanf("%lld", &b);
    points[a][b] = 1;
    points[b][a] = 1;
  }
  for (i = 1; i < n + 1; i++) {
    long long int flag = 1;
    for (j = 1; j < n + 1; j++) {
      if (points[i][j] == 0 && i != j) flag = 0;
    }
    if (flag == 1) {
      value[i] = 2;
    }
  }
  for (i = 1; i < n + 1; i++) {
    for (j = 1; j < n + 1; j++) {
      if (points[i][j] == 0 && i != j) {
        if (value[i] == 0 || value[j] == 0) {
          if (value[i] == 0 && value[j] == 0) {
            value[i] = 1;
            value[j] = 3;
            if (bfs(i) == -1) {
              printf("No\n");
              return 0;
            }
            if (bfs(j) == -1) {
              printf("No\n");
              return 0;
            }
          } else if (value[i] == 0) {
            value[i] = 4 - value[j];
            if (bfs(i) == -1) {
              printf("No\n");
              return 0;
            }
          } else {
            value[j] = 4 - value[i];
            if (bfs(j) == -1) {
              printf("No\n");
              return 0;
            }
          }
        } else if (value[i] == value[j]) {
          printf("No\n");
          return 0;
        }
      }
    }
  }
  if (check() == 0) {
    printf("No\n");
    return 0;
  }
  printf("Yes\n");
  for (i = 1; i < n + 1; i++) {
    if (value[i] == 1)
      printf("a");
    else if (value[i] == 2)
      printf("b");
    else
      printf("c");
  }
  printf("\n");
  return 0;
}
