// Problem: P3369 【模板】普通平衡树
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/P3369
// Memory Limit: 128 MB
// Time Limit: 1000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

//And in that light,I find deliverance.
#include<bits/stdc++.h>
using namespace std;
inline int read(){
   int s=0,w=1;
   char ch=getchar();
   while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
   while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
   return s*w;
}
mt19937 rnd(114514);
struct node{int ls,rs,pri,val,sz,B,C;}a[1000003];
int cnt=1;
void update(int x)
{
	a[x].sz=a[a[x].ls].sz+a[a[x].rs].sz+1;
	a[x].B=a[a[x].ls].B+a[a[x].rs].B+(a[x].val==0);
	a[x].C=a[a[x].ls].C+a[a[x].rs].C+(a[x].val==1);
	return ;
}
void rsplit(int cur,int k,int &x,int &y)
{
	if(!cur) {x=0,y=0;return ;}
	if(a[a[cur].ls].sz>=k)
		y=cur,rsplit(a[cur].ls,k,x,a[y].ls);
	else
		x=cur,rsplit(a[cur].rs,k-a[a[cur].ls].sz-1,a[x].rs,y);
	update(cur);
	return ;
}
int merge(int x,int y)
{
	if(!x||!y) return x+y;
	if(a[x].pri>a[y].pri) 
		return a[y].ls=merge(x,a[y].ls),update(y),y;
	else
		return a[x].rs=merge(a[x].rs,y),update(x),x;
}
int firB(int x)
{
	if(!x) return 0;
	if(a[a[x].ls].B) return firB(a[x].ls);
	if(!a[x].val) return a[a[x].ls].sz;
	return a[a[x].ls].sz+1+firB(a[x].rs);
}
int firC(int x)
{
	if(!x) return 0;
	if(a[a[x].ls].C) return firC(a[x].ls);
	if(a[x].val) return a[a[x].ls].sz;
	return a[a[x].ls].sz+1+firC(a[x].rs);
}
char s[1<<20],t[1<<20];
signed main()
{
	int rt1=0,rt2=0;
	int n=read(),k=read();
	scanf("%s",s+1);
	scanf("%s",t+1);
	int sB=0;
	for(int i=1; i<=n; ++i) if(s[i]=='B') ++sB;
	if(sB>n/2)
	{
		for(int i=1; i<=n; ++i) s[i]^=('B'^'C');
		for(int i=1; i<=n; ++i) t[i]^=('C'^'B');
		sB=n-sB;
	}
	for(int i=1; i<=n; ++i)
	{
		a[i].pri=rnd(),a[i].val=(s[i]=='C'),a[i].sz=1;
		if(s[i]=='C') a[i].C=1;
		else a[i].B=1;
		a[n+i].pri=rnd(),a[n+i].val=(t[i]=='C'),a[n+i].sz=1;
		if(t[i]=='C') a[n+i].C=1;
		else a[n+i].B=1;
		rt1=merge(rt1,i);
		rt2=merge(rt2,n+i);
	}
	int fA=0,fB=0;
	vector<pair<int,int>> ans;
	while(sB--)
	{
		int A=firB(rt1);
		int B=firC(rt2);
		// printf("%d %d\n",A,B);
		int X,Y;
		fA=(fA+A)%n,
		fB=(fB+B)%n;
		rsplit(rt1,A,X,Y),
		rt1=merge(Y,X),
		rsplit(rt2,B,X,Y),
		rt2=merge(Y,X);
		if(k==1)
		{
			rsplit(rt1,1,X,rt1),
			rsplit(rt2,1,Y,rt2),
			rt1=merge(Y,rt1),
			rt2=merge(X,rt2),
			ans.push_back({fA%n+1,fB%n+1});
			continue;
		}
		A=n-k;
		fA=(fA+A)%n,
		rsplit(rt1,A,X,Y),
		rt1=merge(Y,X);
		
		ans.push_back({fA%n+1,fB%n+1});
		ans.push_back({(fA+1)%n+1,fB%n+1});
		int X1,Y1;
		rsplit(rt1,k,X1,rt1);
		rsplit(rt1,1,Y1,rt1);
		int X2,Y2;
		rsplit(rt2,1,X2,rt2);
		rsplit(rt2,k-1,Y2,rt2);
		rt1=merge(merge(X2,X1),rt1);
		rt2=merge(merge(Y2,Y1),rt2);
	}
	printf("%d\n",(int)ans.size());
	for(int i=0; i<n; ++i) s[i]=s[i+1];
	for(int i=0; i<n; ++i) t[i]=t[i+1];
		// for(int i=0; i<n; ++i)
			// putchar(s[i]);
		// puts("");
		// for(int i=0; i<n; ++i)
			// putchar(t[i]);
		// puts("");
	for(auto [x,y]:ans)
	{
		printf("%d %d\n",x,y);
		--x,--y;
		// for(int i=0; i<k; ++i)
			// swap(s[(x+i)%n],t[(y+i)%n]);
		// for(int i=0; i<n; ++i)
			// putchar(s[i]);
		// puts("");
		// for(int i=0; i<n; ++i)
			// putchar(t[i]);
		// puts("");
	}
	return 0;
}