// MagicDark
#include <bits/stdc++.h>
#define debug cerr << "\033[32m[" << __LINE__ << "]\033[0m "
#define SZ(x) ((int) x.size() - 1)
#define all(x) x.begin(), x.end()
#define ms(x, y) memset(x, y, sizeof x)
#define F(i, x, y) for (int i = (x); i <= (y); i++)
#define DF(i, x, y) for (int i = (x); i >= (y); i--)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
template <typename T> T& chkmax(T& x, T y) {return x = max(x, y);}
template <typename T> T& chkmin(T& x, T y) {return x = min(x, y);}
template <typename T> T& read(T &x) {
	x = 0; int f = 1; char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') f = - f;
	for (; isdigit(c); c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
	return x *= f;
}
mt19937 mrand(20071211);//chrono::steady_clock::now().time_since_epoch().count());
// inline int rnd(int l, int r) {return mrand() % (r - l + 1) + l;}
const int N = 6e5 + 10;
int n, k, a[N], b[N];
int ls[N], rs[N], s[N][2], sz[N], rt1, rt2;
bool val[N];
unsigned key[N];
void pushup(int num) {
	sz[num] = sz[ls[num]] + sz[rs[num]] + 1;
	F(i, 0, 1) s[num][i] = s[ls[num]][i] + s[rs[num]][i] + (val[num] == i);
}
int merge(int num1, int num2) {
	if (!num1 || !num2) return num1 ^ num2;
	if (key[num1] < key[num2]) return rs[num1] = merge(rs[num1], num2), pushup(num1), num1;
	return ls[num2] = merge(num1, ls[num2]), pushup(num2), num2;
}
pair <int, int> split(int num, int k) {
	if (!num) return {0, 0};
	if (k >= sz[ls[num]] + 1) {
		auto [a, b] = split(rs[num], k - sz[ls[num]] - 1);
		rs[num] = a;
		pushup(num);
		return make_pair(num, b);
	} else {
		auto [a, b] = split(ls[num], k);
		ls[num] = b;
		pushup(num);
		return make_pair(a, num);
	}
}
// int find1(int x) {
// 	if (sum[ls[x]]) return find1(ls[x]);
// 	if (val[x]) return sz[ls[x]] + 1;
// 	return sz[ls[x]] + 1 + find1(rs[x]);
// }
// int find0(int x) {
// 	if (sum[ls[x]] != sz[ls[x]]) return find0(ls[x]);
// 	if (!val[x]) return sz[ls[x]] + 1;
// 	return sz[ls[x]] + 1 + find0(rs[x]);
// }
int find(int x, bool y) {
	// debug << x << endl;
	if (s[ls[x]][y]) return find(ls[x], y);
	if (val[x] == y) return sz[ls[x]] + 1;
	return sz[ls[x]] + 1 + find(rs[x], y);
}
signed main() {
	read(n), read(k);
	F(i, 1, 2 * n) key[i] = mrand();
	F(i, 1, n) {
		char ch;
		do {
			ch = getchar();
		} while (ch != 'B' && ch != 'C');
		a[i] = ch == 'C';
		s[i][val[i] = a[i]] = 1;
		sz[i] = 1;
		rt1 = merge(rt1, i);
	}
	F(i, 1, n) {
		char ch;
		do {
			ch = getchar();
		} while (ch != 'B' && ch != 'C');
		b[i] = ch == 'C';
		s[i + n][val[i + n] = b[i]] = 1;
		sz[i + n] = 1;
		rt2 = merge(rt2, i + n);
	}
	bool w = s[rt1][1] > s[rt2][1];
	vector <pair <int, int>> ans;
	int s1 = 0, s2 = 0;
	// debug << w << endl;
	while (s[rt1][!w]) {
		// debug << s[rt1][!w] << " " << s[rt2][w] << endl;
		int pos1 = find(rt1, !w), pos2 = find(rt2, w);
		// debug << "% " << pos1 << " " << pos2 << endl;
		pos2 = (pos2 - k - 1 + n) % n + 1;
		if (pos1 > 1) {
			s1 += pos1 - 1;
			auto [a, b] = split(rt1, pos1 - 1);
			rt1 = merge(b, a);
		}
		if (pos2 > 1) {
			s2 += pos2 - 1;
			auto [a, b] = split(rt2, pos2 - 1);
			rt2 = merge(b, a);
		}
		// debug << "OK\n";
		{
			auto [a, b] = split(rt1, 1);
			auto [c, d] = split(b, k - 1);
			// debug << val[a] << endl;
			// assert(val[a] != w);
			s[a][val[a]]--;
			s[a][val[a] ^= true]++;
			rt1 = merge(c, merge(a, d));
		}
		// debug << "OK\n";
		{
			auto [a, b] = split(rt2, k);
			auto [c, d] = split(b, 1);
			// debug << val[c] << endl;
			s[c][val[c]]--;
			s[c][val[c] ^= true]++;
			rt2 = merge(c, merge(a, d));
		}
		ans.emplace_back(s1 + 1, s2 + 1);
		ans.emplace_back(s1 + 1, s2 + 2);
		// int a1, b1, c1;
		// int a2, b2, c2;
		// {
		// 	if (pos1 + k <= n) {
		// 		auto [a, b] = split(rt1, pos1 - 1);
		// 		auto [b, c] = split(b, k);
		// 	}
		// }
	}
	assert(ans.size() <= n);
	cout << ans.size() << '\n';
	for (auto [a, b]: ans) cout << (a - 1) % n + 1 << ' ' << (b - 1) % n + 1 << '\n';
	return 0;
}
/* why?
*/