#include <bits/stdc++.h>
using namespace std;
int p[3][200005], vis[200005], flag[200005], gs, qlt[200005], tim, n, k,
    a[200005], b[200005], t[200005], fa[200005], top, str[200005];
char anss[200005];
void dfs(int x) {
  tim++;
  t[x] = tim;
  fa[x] = t[x];
  vis[x] = 1;
  top++;
  str[top] = x;
  if (p[1][x] + 1 <= n && flag[a[p[1][x] + 1]] == 0) {
    if (t[a[p[1][x] + 1]] > 9999991) {
      dfs(a[p[1][x] + 1]);
      fa[x] = min(fa[x], fa[a[p[1][x] + 1]]);
    } else {
      if (vis[a[p[1][x] + 1]] == 1) fa[x] = min(fa[x], fa[a[p[1][x] + 1]]);
    }
  }
  if (p[2][x] + 1 <= n && flag[b[p[2][x] + 1]] == 0) {
    if (t[b[p[2][x] + 1]] > 9999991) {
      dfs(b[p[2][x] + 1]);
      fa[x] = min(fa[x], fa[b[p[2][x] + 1]]);
    } else {
      if (vis[b[p[2][x] + 1]] == 1) fa[x] = min(fa[x], fa[b[p[2][x] + 1]]);
    }
  }
  if (t[x] == fa[x]) {
    gs++;
    while (t[str[top]] != fa[str[top]]) {
      vis[str[top]] = 0;
      qlt[str[top]] = gs;
      flag[str[top]] = 1;
      top--;
    }
    qlt[str[top]] = gs;
    vis[str[top]] = 0;
    flag[str[top]] = 1;
    top--;
  }
}
int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; i++) {
    int tem;
    cin >> tem;
    a[i] = tem;
    p[1][tem] = i;
  }
  for (int i = 1; i <= n; i++) {
    int tem;
    cin >> tem;
    b[i] = tem;
    p[2][tem] = i;
  }
  for (int i = 1; i <= n; i++) {
    t[i] = 9999999;
  }
  dfs(a[1]);
  for (int i = 1; i <= n; i++) {
    if (gs - qlt[i] > 25)
      anss[i] = 'z';
    else
      anss[i] = gs - qlt[i] + 'a';
  }
  if (gs >= k) {
    cout << "YES" << endl;
    for (int i = 1; i <= n; i++) cout << anss[i];
  } else
    cout << "NO";
}
