#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define uint unsigned int
#define ldb long double
#define pii pair<int,int>
#define mkp make_pair
#define mkt make_tuple
#define fr first
#define se second
#define uset unordered_set
#define umap unordered_map
#define pqueue priority_queue
#define all(_box) _box.begin(),_box.end()
#define ppc __builtin_popcount
#define ctz __builtin_ctz
#define clz __builtin_clz
#define lbd lower_bound
#define ubd upper_bound
#define deb(x) cerr<<#x<<'='<<(x)<<' '
using namespace std;
mt19937 rng(random_device{}());
const int inf=0x3f3f3f3f;
const int N=3e5+4;
int n,k;
string s,t;
vector<pii>ans;

bool rbool(int p,int q){
    return uniform_int_distribution<int>(1,q)(rng)<=p;
}

int rot1,rot2;
namespace FHQ{
    int cnt;
    struct node{
        int ls,rs,siz,pos,fp;
        node(){
            ls=rs=siz=0;
            pos=fp=inf;
        }
        node(bool f){
            ls=rs=0;
            siz=1;
            pos=fp=f?0:inf;
        }
    }st[N];

    #define ls(id) st[id].ls
    #define rs(id) st[id].rs
    void push_up(int id){
        st[id].siz=st[ls(id)].siz+1+st[rs(id)].siz;
        st[id].fp=min({
            inf,
            st[ls(id)].fp,
            st[ls(id)].siz+st[id].pos,
            st[ls(id)].siz+1+st[rs(id)].fp
        });
    }
    void split(int id,int key,int &p,int &q){
        if(!id){
            p=q=0;
            return;
        }
        if(st[ls(id)].siz+1<=key){
            p=id,key-=st[ls(id)].siz+1;
            split(rs(id),key,rs(p),q);
        }
        else{
            q=id;
            split(ls(id),key,p,ls(q));
        }
        push_up(id);
    }
    int merge(int p,int q){
        if(!p||!q)return p|q;
        if(rbool(st[p].siz,st[p].siz+st[q].siz)){
            rs(p)=merge(rs(p),q);
            push_up(p);
            return p;
        }
        else{
            ls(q)=merge(p,ls(q));
            push_up(q);
            return q;
        }
    }
    #undef ls
    #undef rs
    void insert(int &rot,int pos,int cur){
        int p,q;
        split(rot,pos,p,q);
        rot=merge(merge(p,cur),q);
    }
    int erase(int &rot,int pos){
        int p,q,p1,p2;
        split(rot,pos+1,p,q);
        split(p,pos,p1,p2);
        rot=merge(p1,q);
        return p2;
    }
}
using FHQ::insert;
using FHQ::erase;

void build(){
    using namespace FHQ;
    for(char c:s){
        int cur=++cnt;
        st[cur]=node(c!='B');
        rot1=merge(rot1,cur);
    }
    for(char c:t){
        int cur=++cnt;
        st[cur]=node(c!='C');
        rot2=merge(rot2,cur);
    }
}
void perform(int p1,int p2){
    ans.push_back({p1,(p2-k+n)%n});
    ans.push_back({p1,(p2-k+n+1)%n});
    int x=erase(rot1,p1);
    int y=erase(rot2,p2);
    FHQ::st[x]=FHQ::st[y]=FHQ::node(0);
    if(p1+k-1>=n)
        insert(rot1,n-2,erase(rot1,0));
    insert(rot1,(p1+k-1)%n,y);
    if(p2-k<0)
        insert(rot2,0,erase(rot2,n-2));
    insert(rot2,(p2-k+n)%n,x);
}
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);

    cin>>n>>k>>s>>t;
    bool rev=0;
    if(2*count(all(s),'B')<n)rev=1,swap(s,t);
    build();

    while(FHQ::st[rot1].fp!=inf){
        assert(FHQ::st[rot2].fp!=inf);
        perform(FHQ::st[rot1].fp,FHQ::st[rot2].fp);
    }

    cout<<ans.size()<<'\n';
    for(auto i:ans){
        if(rev)swap(i.fr,i.se);
        cout<<i.fr+1<<' '<<i.se+1<<'\n';
    }
}