#include <map>
#include <set>
#include <array>
#include <cmath>
#include <deque>
#include <bitset>
#include <random>
#include <string>
#include <vector>
#include <cassert>
#include <complex>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>

using namespace std;


int n, k;

struct holder {
  int ptr;
  int ind;
  set<int> st;
  int add;

  holder(): ptr(n - 1), ind(n - 1), add(0) {}

  void move_ptr() {
    while (st.count(ind - add)) {
      st.erase(ind - add);
      --ind;
    }
    --ptr;
  }

  void swap(int where) {
    ++add;
    st.insert(ind - (k - where) - add);
    move_ptr();
  }

  void skip() {
    --ind;
    move_ptr();
  }
};

int norm(int i) {
  i = (i % n + n) % n;
  return i + 1;
}


int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  cin >> n >> k;
  array<string, 2> s;
  cin >> s[0] >> s[1];
  int cnt = 0;
  for (char ch : s[0]) {
    cnt += (ch == 'B');
  }

  if (cnt * 2 < n) {
    for (char& ch : s[0]) {
      ch = 'B' + 'C' - ch;
    }
    for (char& ch : s[1]) {
      ch = 'B' + 'C' - ch;
    }
  }

  vector<array<int, 2>> ans;

  holder dir, rev;
  while (dir.ptr >= 0 && rev.ptr >= 0) {
    while (dir.ptr >= 0 && s[0][dir.ptr] == 'B') dir.skip();
    while (rev.ptr >= 0 && s[1][n - 1 - rev.ptr] == 'C') rev.skip();
    if (dir.ptr < 0 || rev.ptr < 0) break;
    /// cerr << dir.ind << " " << dir.ptr << " " << rev.ind << " " << rev.ptr << endl;
    ans.push_back({dir.ind - k, n - 1 - rev.ind});
    ans.push_back({dir.ind - k + 1, n - 1 - rev.ind});
    dir.swap(0);
    rev.swap(1);
  }

  cout << ans.size() << "\n";
  for (auto elem : ans) {
    cout << norm(elem[0]) << " " << norm(elem[1]) << "\n";
  }

  
  return 0;
}