#include <bits/stdc++.h>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define piii pair<int, pii>
#define plll pair<long long, pll>
#define tiii array<int, 3>
#define tiiii array<int, 4>
#define ff first
#define ss second
#define ee ss.ff
#define rr ss.ss
typedef long long ll;
typedef long double ld;
const int INF = (int)1e9 + 7;

using namespace std;

int n, k;
int A[303030];
int B[303030];

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);

	cin >> n >> k;
	for(int i = 0; i < n; ++i)
	{
		char c; cin >> c;
		A[i] = (c == 'B');
	}
	for(int i = 0; i < n; ++i)
	{
		char c; cin >> c;
		B[i] = (c == 'B');
	}
	
	int cnt = 0;
	for(int i = 0; i < n; ++i) if(A[i]) ++cnt;
	bool f = (cnt <= n / 2);

	vector<int> C, D;
	for(int i = 0; i < n; ++i) if(A[i] == f) C.push_back(i);
	for(int i = n - 1; i >= 0; --i) if(B[i] != f) D.push_back(i);
	int t = C.size();
	assert(t == D.size());

	vector<int> E, F;
	vector<pii> G;
	for(int i = 0; i < t; ++i)
	{
		int x = C[i] + (E.end() - lower_bound(E.begin(), E.end(), -C[i] - k));
		int y = D[i] - (F.end() - lower_bound(F.begin(), F.end(), D[i] - k + 1));
		E.push_back(-x);
		F.push_back(y);
		G.push_back({x, y});
	}

	cout << 2 * t << '\n';
	for(auto [x, y] : G)
	{
		cout << (n + x - k) % n + 1 << ' ' << y + 1 << '\n';
		cout << (n + x - k + 1) % n + 1 << ' ' << y + 1 << '\n';
	}
}