#include <bits/stdc++.h>

using std::bitset;
using std::cin, std::cout, std::endl, std::flush, std::cerr;
using std::min, std::max;
using std::optional;
using std::pair, std::tuple;
using std::set, std::map, std::multiset;
using std::tie, std::swap;
using std::vector, std::array, std::queue, std::deque, std::string;
using std::views::iota, std::views::reverse;

template <class A> constexpr int sz(A&& a) {
    return int(std::size(std::forward<A>(a)));
}

using i32 = int32_t;
using i64 = int64_t;

auto mt =
    std::mt19937(std::chrono::steady_clock::now().time_since_epoch().count());

template <class T> using Vec = std::vector<T>;

template <class M, bool persistent = false> struct TreapManager {
    using S = typename M::S;
    using F = typename M::F;

    TreapManager(M m_, int alloc = 0) : m(m_) {
        if (alloc > 0) {
            nodes.reserve(alloc);
        } else {
            // make sure to understand what you're doing
            assert(!persistent);
        }

        for (int z = 0; z < 2; z++) {
            states[z] = uint32_t(mt());
        }
    }

    using Tree = int;

    Tree make_empty() { return Tree(null); }

    Tree make_single(S s) {  /// start-hash
        int i = int(nodes.size());
        nodes.push_back(Node{null, null, 1, s, s});
        return i;
    }  /// end-hash

    Tree make_copy(Tree o) { return _make_copy(o); }

    int size(const Tree t) { return _size(t); }
    int apply(Tree t, F f) { return _apply(t, f); }
    S prod(const Tree& t) { return _prod(t); }

    Tree split_k(Tree& t, int k) {  /// start-hash
        Tree o;
        tie(t, o) = _split_k(t, k);
        return o;
    }  /// end-hash

    Tree merge(Tree a, Tree b) { return _merge(a, b); }

    Tree build(const Vec<S>& a) {  /// start-hash
        if (a.empty()) return make_empty();
        return _build(a, 0, int(a.size()));
    }  /// end-hash

    Vec<S> to_array(const Tree& t) {  /// start-hash
        Vec<S> buf;
        buf.reserve(size(t));
        _to_array(t, buf);
        return buf;
    }  /// end-hash

  private:
    static constexpr int null = -42;
    M m;

    struct Node {  /// start-hash
        int li, ri, sz;
        S a, s;
    };
    Vec<Node> nodes;
    Node& node(int i) { return nodes[i]; }
    int _size(int i) { return i == null ? 0 : node(i).sz; }  /// end-hash

    int _make_copy(int o) {  /// start-hash
        if constexpr (!persistent) return o;

        if (o == null) return null;
        assert(nodes.size() < nodes.capacity());
        int i = int(nodes.size());
        nodes.push_back(node(o));
        return i;
    }  /// end-hash

    int _build(const Vec<S>& a, int l, int r) {  /// start-hash
        if (r - l == 1) {
            return make_single(a[l]);
        }
        int md = (l + r) / 2;
        return _merge(_build(a, l, md), _build(a, md, r));
    }  /// end-hash

    void _update(int i) {  /// start-hash
        auto& n = node(i);
        n.s = m.op(_prod(n.li), m.op(n.a, _prod(n.ri)));
        n.sz = size(n.li) + size(n.ri) + 1;
    }  /// end-hash

    S _prod(int i) { return i == null ? m.e() : node(i).s; }

    int _apply(int i, F f) {  /// start-hash
        if (i == null) return i;
        i = _make_copy(i);
        auto& n = node(i);
        n.app = true;
        return i;
    }  /// end-hash

    int downdate(int i) {  /// start-hash
        assert(i != null);
        return _make_copy(i);
    }  /// end-hash

    template <class F> pair<int, int> _split(int i, F go_left) {  /// start-hash
        if (i == null) return {null, null};
        i = downdate(i);
        auto& n = node(i);
        int li = n.li, ri = n.ri;
        int x, y;
        if (go_left(li, ri)) {
            y = i;
            tie(x, n.li) = _split(n.li, go_left);
        } else {
            x = i;
            tie(n.ri, y) = _split(n.ri, go_left);
        }
        _update(i);
        return {x, y};
    }  /// end-hash

    pair<int, int> _split_k(int i, int k) {  /// start-hash
        return _split(i, [&](int li, int) -> bool {
            int lsz = size(li);
            if (k <= lsz) {
                return true;
            } else {
                k -= lsz + 1;
                return false;
            }
        });
    }  /// end-hash

    // Use std::mt19937_64 if performance is not an issue
    // https://prng.di.unimi.it/xoroshiro64star.c
    inline uint32_t rotl(const uint32_t x, int k) {  /// start-hash
        return (x << k) | (x >> (32 - k));
    }
    uint32_t states[2];
    uint32_t rng() {
        const uint32_t s0 = states[0];
        uint32_t s1 = states[1];
        const uint32_t res = s0 * 0x9E3779BB;
        s1 ^= s0;
        states[0] = rotl(s0, 26) ^ s1 ^ (s1 << 9);
        states[1] = rotl(s1, 13);
        return res;
    }  /// end-hash

    int _merge(int a, int b) {  /// start-hash
        if (a == null) return b;
        if (b == null) return a;
        int r;
        uint32_t sa = size(a), sb = size(b);
        if (rng() % (sa + sb) < sa) {
            r = downdate(a);
            node(r).ri = _merge(node(r).ri, b);
        } else {
            r = downdate(b);
            node(r).li = _merge(a, node(r).li);
        }
        _update(r);
        return r;
    }  /// end-hash

    void _to_array(int i, Vec<S>& buf) {  /// start-hash
        if (i == null) return;
        downdate(i);
        auto& n = node(i);
        _to_array(n.li, buf);
        buf.push_back(n.a);
        _to_array(n.ri, buf);
    }  /// end-hash
};

int main() {
    std::ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << std::fixed << std::setprecision(20);

    int N, K;
    string A, B;
    cin >> N >> K >> A >> B;
    {
        int balance = 0;
        for (char c : A) {
            if (c == 'B') {
                balance++;
            } else if (c == 'C') {
                balance--;
            } else {
                assert(false);
            }
        }

        if (balance > 0) {
            for (char& c : A) {
                c ^= 'B' ^ 'C';
            }
            for (char& c : B) {
                c ^= 'B' ^ 'C';
            }
        }
    }

    constexpr int INF = 1e8;
    struct Monoid {
        struct S {
            int offset;
            bool color;
            array<int, 2> locs;
        };
        using F = char;  // dummy

        S single(char x) {
            bool color = (x != 'B');
            auto s = S{};
            s.offset = 1;
            s.color = color;
            s.locs[color] = 0;
            s.locs[1 - color] = INF;
            return s;
        }

        S e() { return S{.offset = 0, .color = false, .locs = {INF, INF}}; }
        S op(S a, S b) {
            return S{.offset = a.offset + b.offset,
                     .color = false,  // don't care
                     .locs = {
                         min(a.locs[0], a.offset + b.locs[0]),
                         min(a.locs[1], a.offset + b.locs[1]),
                     }};
        }
    };

    auto m = Monoid();
    auto tm = TreapManager(m, 2 * N);
    using Tree = decltype(tm)::Tree;
    auto ta = tm.make_empty();
    auto tb = tm.make_empty();
    for (int i : iota(0, N)) {
        ta = tm.merge(ta, tm.make_single(m.single(A[i])));
        tb = tm.merge(tb, tm.make_single(m.single(B[i])));
    }

    auto ops = Vec<pair<int, int>>{};
    ops.reserve(N);
    auto do_rotate = [&](Tree t, int k) -> Tree {
        Tree o = tm.split_k(t, k);
        return tm.merge(o, t);
    };
    auto do_swap = [&](int i, int j) {
        i = (i % N + N) % N;
        j = (j % N + N) % N;
        ops.emplace_back(i, j);
        ta = do_rotate(ta, i);
        tb = do_rotate(tb, j);
        int a, b, c, d;
        a = ta, c = tb;
        b = tm.split_k(a, K);
        d = tm.split_k(c, K);
        ta = tm.merge(c, b);
        tb = tm.merge(a, d);
        ta = do_rotate(ta, N - i);
        tb = do_rotate(tb, N - j);
    };

    while (true) {
        auto i = tm.prod(ta).locs[0];
        auto j = tm.prod(tb).locs[1];
        if (i == INF) break;
        do_swap(i - K, j);
        do_swap(i - K + 1, j);
    }

    cout << ops.size() << '\n';
    for (auto [i, j] : ops) {
        cout << i + 1 << ' ' << j + 1 << '\n';
    }

    return 0;
}