#include <bits/stdc++.h>
#define cs const
#define pb push_back
using namespace std;
using pi = pair <int, int> ; 
mt19937 rnd(18848585);
cs int N = 1e6 + 5; 

int n, k;
char A[N], B[N]; 
struct FHQ {
    int root, cc; 
    struct hh { int co, sb, sc, pri, ch[2], size; } tr[N];
    #define lc(x) tr[x].ch[0]
    #define rc(x) tr[x].ch[1]
    void pushup(int x) {
        tr[x].size = 1 + tr[lc(x)].size + tr[rc(x)].size;
        tr[x].sb = (!tr[x].co) + tr[lc(x)].sb + tr[rc(x)].sb; 
        tr[x].sc = tr[x].co + tr[lc(x)].sc + tr[rc(x)].sc; 
    }
    int newnode(int co) {
        ++ cc; 
        tr[cc].co = co; 
        tr[cc].pri = rnd(); 
        pushup(cc);
        return cc; 
    }
    int merge(int x, int y) {
        if(!x || !y) return x + y; 
        if(tr[x].pri < tr[y].pri) return rc(x) = merge(rc(x), y), pushup(x), x; 
        return lc(y) = merge(x, lc(y)), pushup(y), y; 
    }
    void split(int x, int k, int & a, int & b) {
        if(!x) return a = b = 0, void();
        if(k <= tr[lc(x)].size) b = x, split(lc(x), k, a, lc(x));
        else k -= tr[lc(x)].size + 1, a = x, split(rc(x), k, rc(x), b);
        pushup(x);
    }
    void ins(int k, int co) {
        int a = 0, b = 0;
        split(root, k, a, b);
        int x = newnode(co); 
        root = merge(a, x);
        root = merge(root, b);
    }
    void del(int k) {
        int a = 0, b = 0;
        split(root, k - 1, a, b);
        int c = 0, d = 0; 
        split(b, 1, c, d);
        root = merge(a, d);
    }
    int find0(int x) {
        // cout << x << ' ' << tr[x].sb << ' ' << tr[x].size << endl;
        if(tr[lc(x)].sb) return find0(lc(x));
        if(tr[x].co == 0) return 1 + tr[lc(x)].size; 
        return tr[lc(x)].size + 1 + find0(rc(x));
    }
    int find1(int x) {
        if(tr[lc(x)].sc) return find1(lc(x));
        if(tr[x].co == 1) return 1 + tr[lc(x)].size; 
        return tr[lc(x)].size + 1 + find1(rc(x));
    }
    void rot(int k) {
        int a = 0, b = 0;
        split(root, k - 1, a, b);
        root = merge(b, a);
    }
    void output(int x) {
        if(!x) return;
        output(lc(x));
        cout << tr[x].co;
        output(rc(x));
    }
} T1, T2;

void mdf(int x, int y) {
    for(int i = 0; i < k; i++) {
        swap(A[(x + i - 1) % n + 1], B[(y + i - 1) % n + 1]);
    }
}
int main() {
    #ifdef zqj
    freopen("1.in","r",stdin);
    #endif
    // ios :: sync_with_stdio(0), cin.tie(0);
    cin >> n >> k;
    scanf("%s%s", A + 1, B + 1);
    int c1 = 0, c2 = 0; 
    for(int i = 1; i <= n; i++) c1 += A[i] == 'B', c2 += A[i] == 'C';
    char o = c1 > c2 ? 'B' : 'C';
    // cout << o << endl;
    for(int i = 1; i <= n; i++) 
        T1.root = T1.merge(T1.root, T1.newnode(A[i] == o));
    for(int i = 1; i <= n; i++)
        T2.root = T2.merge(T2.root, T2.newnode(B[i] == o));

    // cout << T1.root << ' ' << T2.root << ' ' << T1.tr[T1.root].size << ' ' << T2.tr[T2.root].size << endl;
    //     T1.output(T1.root);cout<<endl;
    //     T2.output(T2.root);cout<<endl;

    vector <pi> ans; 
    int shx = 0, shy = 0; 
    while(1) {
        if(T1.tr[T1.root].sb == 0) break;
        assert(T1.tr[T1.root].sb == T2.tr[T2.root].sc);
        int x = T1.find0(T1.root);
        int y = T2.find1(T2.root);
        y = (y - 1 - k + n) % n + 1; 
        // cout << "FFFF " << x << ' ' << y << endl;
        if(x > 1) T1.rot(x), shx += x - 1; 
        if(y > 1) T2.rot(y), shy += y - 1; 
        shx %= n; 
        shy %= n;
        // T1.output(T1.root);cout<<endl;
        // T2.output(T2.root);cout<<endl;
        ans.pb({shx + 1, shy + 1});
        ans.pb({shx + 1, shy + 2});

        T1.del(1);
        T1.ins(k - 1, 1);
        T2.del(k + 1);
        T2.ins(0, 0);
        // T1.output(T1.root);cout<<endl;
        // T2.output(T2.root);cout<<endl;
        // exit(0);
    }
    cout << ans.size() << '\n';
    for(auto [x, y] : ans) {
        x = (x - 1) % n + 1; 
        y = (y - 1) % n + 1;
        cout << x << ' ' << y << '\n';
        #ifdef zqj
        mdf(x, y);
        #endif
    }
    #ifdef zqj
    for(int i = 1; i <= n; i++) cout << A[i]; cout << endl;
    for(int i = 1; i <= n; i++) cout << B[i]; cout << endl;
    #endif
    return 0; 
}