#include <bits/stdc++.h>
using namespace std;

int n,k;
string strA,strB;
vector<pair<int,int>> ans;

int main(){
	ios_base::sync_with_stdio(false);
	cin >> n >> k;
	cin >> strA >> strB;
	char colA='B';
	char colB='C';
	
	int sum=0;
	for (auto ch:strA) if (ch==colA) sum++;
	if (sum<n/2){
		swap(colA,colB);
		sum=n-sum;
	}
	
	deque<char> qA,qB;
	int stA=0,edA=k,stB=0,edB=k-1;
	for (int i=0;i<k+1;i++) qA.push_back(strA[i]);
	for (int i=0;i<k;i++) qB.push_back(strB[i]);
	for (;sum<n;sum++){
		for (;qA.front()==colA;){
			stA=(stA+1)%n;
			edA=(edA+1)%n;
			qA.pop_front();
			qA.push_back(strA[edA]);	
		}
		for (;qB.back()==colB;){
			stB=(stB+1)%n;
			edB=(edB+1)%n;
			qB.pop_front();
			qB.push_back(strB[edB]);	
		}
		ans.emplace_back((stA+1)%n,stB);
		ans.emplace_back(stA,stB);
		qB.push_front(qA.front());
		qA.pop_front();
		qA.push_back(qB.back());
		qB.pop_back();
	}
	
	cout << (int)ans.size() << "\n";
	for (auto [x,y]:ans){
		cout << x+1 << " " << y+1 << "\n";	
	}
	return 0;
}