#include <bits/stdc++.h>
using namespace std;
constexpr int SIZE = (int)1e6;
int n, k, from, to;
vector<int> g[SIZE], h[SIZE];
vector<int> ord;
vector<bool> check;
string ans;
int component[SIZE];
int comp;
void dfs1(int v) {
  check[v] = true;
  for (int i : g[v]) {
    if (!check[i]) {
      dfs1(i);
    }
  }
  ord.push_back(v);
}
void dfs2(int v) {
  check[v] = true;
  component[v] = comp;
  for (int i : h[v]) {
    if (!check[i]) {
      dfs2(i);
    }
  }
}
int main() {
  cin >> n >> k;
  for (int j = 0; j < 2; j++) {
    cin >> from;
    from--;
    for (int i = 1; i < n; i++) {
      cin >> to;
      to--;
      g[from].push_back(to);
      h[to].push_back(from);
      from = to;
    }
  }
  check.resize(n, false);
  for (int i = 0; i < n; i++) {
    if (!check[i]) {
      dfs1(i);
    }
  }
  for (int i = 0; i < n; i++) {
    check[i] = false;
  }
  for (int i = ord.size() - 1; i >= 0; i--) {
    if (!check[ord[i]]) {
      dfs2(ord[i]);
      comp++;
    }
  }
  if (comp < k) {
    cout << "NO";
    return 0;
  }
  ans.resize(n);
  cout << "YES" << endl;
  for (int i = 0; i < ans.size(); i++) {
    if (k - 1 < component[i]) {
      ans[i] = char('a' + k - 1);
    } else {
      ans[i] = char('a' + component[i]);
    }
  }
  cout << ans;
  return 0;
}
