#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
int n, k, p[2][N], vis[N], cnt, ans[N];
vector<int> go[N], to[N];
void read_input() {
  cin >> n >> k;
  for (int i = 0; i < 2; i++)
    for (int j = 0; j < n; j++) {
      cin >> p[i][j];
      p[i][j]--;
      if (j > 0) {
        go[p[i][j]].push_back(p[i][j - 1]);
        to[p[i][j - 1]].push_back(p[i][j]);
      }
    }
}
void dfs(int u, vector<int> *adj, vector<int> &vec) {
  vis[u] = 1;
  for (int v : adj[u])
    if (vis[v] == false) dfs(v, adj, vec);
  vec.push_back(u);
}
void kosaraju() {
  vector<int> ord;
  for (int u = 0; u < n; u++)
    if (vis[u] == false) dfs(u, go, ord);
  memset(vis, 0, sizeof vis);
  reverse(ord.begin(), ord.end());
  for (int u : ord)
    if (vis[u] == false) {
      vector<int> comp;
      dfs(u, to, comp);
      for (int u : comp) ans[u] = cnt;
      cnt++;
    }
}
void write_output() {
  if (cnt < k) {
    cout << "NO" << endl;
    return;
  }
  cout << "YES" << endl;
  for (int i = 0; i < n; i++) cout << char(min(cnt - ans[i], k) - 1 + 'a');
  cout << endl;
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0);
  read_input(), kosaraju(), write_output();
}
