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

typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<pii> vpii;
typedef complex<double> cpx;
template <typename T> using minPq = priority_queue<T, vector<T>, greater<T>>;
#define ms(a, x) memset(a, x, sizeof(a))
#define pb push_back
#define fs first
#define sn second
#define ALL(v) begin(v), end(v)
#define SZ(v) ((int) (v).size())
#define lbv(v, x) (lower_bound(ALL(v), x) - (v).begin())
#define ubv(v, x) (upper_bound(ALL(v), x) - (v).begin())
template <typename T> inline void UNIQUE(vector<T> &v){sort(ALL(v)); v.resize(unique(ALL(v)) - v.begin());}
const int INF = 0x3f3f3f3f;
const ll LLINF = 0x3f3f3f3f3f3f3f3f;
const double PI = acos(-1);
#define FR(i, n) for(int i = 0; i < (n); i++)
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define FORR(i, a, b) for(int i = (a); i >= (b); i--)
#define dbg(x) {cerr << #x << ' ' << x << endl;}
#define dbgArr(arr, n) {cerr << #arr; FR(_i, n) cerr << ' ' << (arr)[_i]; cerr << endl;}
template <typename T, typename U>
ostream& operator<<(ostream &os, pair<T, U> p){return os << "(" << p.fs << ", " << p.sn << ")";}

struct Str {
    vi cuts;
    bool init;
};

void swap(Str &a, int ai, Str &b, int bi){
    assert(ai > 0 || bi > 0);

    vi vec1e, vec2e;
    FOR(i, ai, SZ(a.cuts)-1) vec1e.pb(a.cuts[i+1] - a.cuts[i]);
    FOR(i, bi, SZ(b.cuts)-1) vec2e.pb(b.cuts[i+1] - b.cuts[i]);
    int aLst = a.cuts[ai] - a.cuts[max(0, ai-1)];
    int bLst = b.cuts[bi] - b.cuts[max(0, bi-1)];
    a.cuts.resize(ai);
    b.cuts.resize(bi);

    if(!ai) a.cuts.pb(0);
    else if(vec2e.empty()) vec2e.pb(aLst);
    else vec2e[0] += aLst;

    if(!bi) b.cuts.pb(0);
    else if(vec1e.empty()) vec1e.pb(bLst);
    else vec1e[0] += bLst;

    for(int s : vec2e) a.cuts.pb(a.cuts.back() + s);
    for(int s : vec1e) b.cuts.pb(b.cuts.back() + s);

    if(!ai) a.init = b.init, b.init ^= bi & 1;
    if(!bi) b.init = a.init, a.init ^= ai & 1;

    swap(a.cuts, b.cuts);
}

Str toBlk(const string &s){
    Str res = {{0}, s[0] == 'b'};
    FOR(i, 1, SZ(s)) if(s[i] != s[i-1]) res.cuts.pb(i);
    res.cuts.pb(SZ(s));
    return res;
}

vpii ans;
Str a, b;

void proc(){
    if(SZ(a.cuts) < SZ(b.cuts)){
        swap(a, b);
        proc();
        swap(a, b);
        swap(ans.back().fs, ans.back().sn);
        return;
    }
    assert(SZ(a.cuts) >= 2);
    assert(SZ(b.cuts) >= 2);

    int ai, bi;

    if(SZ(b.cuts) == 2){
        ai = SZ(a.cuts)/2;
        bi = 1;
        // dbg(ai);
        // dbg(bi);
        // dbg(a.init);
        // dbg(b.init);
        if((a.init ^ b.init) == ((ai^bi) & 1)) bi--;
    }
    else {
        bi = SZ(b.cuts)-2;
        ai = SZ(a.cuts)-2;
        if((a.init ^ b.init) == ((ai^bi) & 1)) ai--;

        loopStart:;
        // cerr << ai << ' ' << bi << endl;
        int asz = ai;
        int bsz = bi + (SZ(a.cuts)-2-ai);
        if(asz > bsz+1){ai -= 2; goto loopStart;}
    }

    assert(ai >= 0);
    assert(bi >= 0);
    ans.pb({a.cuts[ai], b.cuts[bi]});
    swap(a, ai, b, bi);
}

int main(){
    cin.sync_with_stdio(0); cin.tie(0);
    string s1, s2;
    cin >> s1 >> s2;

    a = toBlk(s1), b = toBlk(s2);
    while(true){
        if(SZ(a.cuts) == 2 && SZ(b.cuts) == 2) break;
        proc();
    }

    cout << SZ(ans) << '\n';
    for(auto [x, y] : ans) cout << x << ' ' << y << '\n';
}