/********include********/
#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#define popcount __builtin_popcount
using namespace std;
//#include <atcoder/all>

/***/
//#include <iomanip>
//#include <cmath>
#include <bits/stdc++.h>


/********define********/
const int MAX = 510000;
const int MOD = 1000000007;

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}


#define rep(i,x) for(long long i=0;i<x;i++)
#define repn(i,x) for(long long i=1;i<=x;i++)
#define rrep(i,x) for(long long i=x-1;i>=0;i--)
#define rrepn(i,x) for(long long i=x;i>1;i--)
#define REP(i,n,x) for(long long i=n;i<x;i++)
#define REPN(i,n,x) for(long long i=n+1;i<x;i++)

#define pr printf
#define re return
#define mod 1000000007
//#define mod 998244353
#define inf  INT_MAX//19桁
#define INF 1e18+5//19桁
const double PI=3.14159265358979323846;
#define fi first
#define se second
#define MAX(a,b) (((a)>(b))?(a):(b))
#define MIN(a,b) (((a)<(b))?(a):(b))
#define all(x) (x).begin(),(x).end()

typedef long long int ll;
typedef pair<long long, long long> P;

/********128bit CFではコンパイルNG********/
/*
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
	std::ostream::sentry s(dest);
	if (s) {
		__uint128_t tmp = value < 0 ? -value : value;
		char buffer[128];
		char *d = std::end(buffer);
		do {
			--d;
			*d = "0123456789"[tmp % 10];
			tmp /= 10;
		} while (tmp != 0);
		if (value < 0) {
			--d;
			*d = '-';
		}
		int len = std::end(buffer) - d;
		if (dest.rdbuf()->sputn(d, len) != len) {
			dest.setstate(std::ios_base::badbit);
		}
	}
	return dest;
}

__int128 parse(string &s) {
	__int128 ret = 0;
	for (int i = 0; i < s.length(); i++)
	if ('0' <= s[i] && s[i] <= '9')
		ret = 10 * ret + s[i] - '0';
	return ret;
}
*/

/********よく使う関数********/

// 素因数分解
vector<pair<long long, long long> > prime_factorize(long long n) {
	vector<pair<long long, long long> > res;
	for (long long p = 2; p * p <= n; ++p) {
		if (n % p != 0) continue;
		int num = 0;
		while (n % p == 0) { ++num; n /= p; }
		res.push_back(make_pair(p, num));
	}
	if (n != 1) res.push_back(make_pair(n, 1));
	return res;
}

// 約数列挙
vector<long long> calc_divisor(long long n) {
	vector<long long> res;
	for (long long i = 1LL; i*i <= n; ++i) {
		if (n % i == 0) {
			res.push_back(i);
        	long long j = n / i;
        	if (j != i) res.push_back(j);
		}
	}
	sort(res.begin(), res.end());
	return res;
}

//最大公約数
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

//最大公約数 複数個
ll gcd(const vector<ll> &v) {
	ll ret = v[0];
	for (ll i = 1; i < v.size(); i++)
		ret = gcd(ret, v[i]);
	return ret;
}

//最小公倍数
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

//最小公倍数 複数個
ll lcm(const vector<ll> &v) {
	ll ret = v[0];
	for (ll i = 1; i < v.size(); i++)
		ret = lcm(ret, v[i]);
	return ret;
}

/*
//大文字→小文字
void to_lower(string &x) {
  for (ll i = 0; i < x.length(); i++) if ('A' <= x[i] && x[i] <= 'Z') {
    x[i] -= 'A' - 'a';
  }
}

//小文字→大文字
void to_bigger(string& x) {
  for (ll i = 0; i < x.length(); i++) if ('a' <= x[i] && x[i] <= 'z') {
    x[i] += 'A' - 'a';
  }
} 
*/

//プライオリティを使ったダイクストラ
/*
#define MAX_V 901
//vector<edge>G[MAX_V];
vector<edge>G[MAX_V];
double d[MAX_V];
struct edge{double to;
            double cost;
			double sum;
			double num;
};

void pri_dijkstra(int s){
	fill(d,d+V,INF);
	d[s]=0;
	priority_queue<P,vector<P>,greater<P>>que;	
	que.push(P(0,s));
	while(!que.empty()){
		P p=que.top();
		que.pop();
		int v=p.second;
		if(d[v]<p.first)continue;
		for(int i=0;i<G[v].size();i++){
			edge e=G[v][i];
			if(d[(ll)e.to]>d[v]+e.cost){
				d[(ll)e.to]=d[v]+e.cost;
				que.push(P(d[(ll)e.to],e.to));
			}
		}
	}
}
*/

int prime[5000005];
bool is_prime[5000005+1];


//エラトステネスの篩
int sieve(int n){
	int p=0;
	for(int i=0;i<=n;i++)is_prime[i]=true;
	is_prime[0]=is_prime[1]=false;
	for(int i=2;i<=n;i++){
		if(is_prime[i]){
			prime[p++]=i;
			for(int j=2*i;j<=n;j+=i)is_prime[j]=false;
		}
	}
	return p;
}

//v(10進数)からbase進数へ変換
template<typename TypeInt>
std::string Itoa(const TypeInt v, int base)
{
    static const char table[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    string ret;
    static numeric_limits<TypeInt> t;
    TypeInt n = v;
    if (t.is_signed) {
        if (v < 0) n *= -1;
    }

    while (n >= base) {
        ret += table[n%base];
        n /= base;
    }
    ret += table[n];
    if (t.is_signed) {
        if (v < 0 && base == 10) ret += '-';
    }
    // 文字列の順番を逆にする
    std::reverse(ret.begin(), ret.end());

    return ret;
}

//10^5 mod 4の場合 n=10, k=5, m=4

ll powmod(ll n, ll k, ll m){
    ll ret = 1;
    while(k){
        if(k&1)ret=ret*n%m;
        n=n*n%m;
        k>>=1;
    }
    return ret;
}

//セグ木
/*
struct SegmentTree {
private:
    int n;
    vector<int> node;

public:
    SegmentTree(vector<int> v) {
        int sz = v.size();
        n = 1; while(n < sz) n *= 2;
        node.resize(2*n-1, inf);
        for(int i=0; i<sz; i++) node[i+n-1] = v[i];
        for(int i=n-2; i>=0; i--) node[i] = min(node[2*i+1], node[2*i+2]);
    }

    void update(int x, int val) {
        x += (n - 1);
        node[x] = val;
        while(x > 0) {
            x = (x - 1) / 2;
            node[x] = min(node[2*x+1], node[2*x+2]);
        }
    }

    int getmin(int a, int b, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        if(r <= a || b <= l) return inf;
        if(a <= l && r <= b) return node[k];

        int vl = getmin(a, b, 2*k+1, l, (l+r)/2);
        int vr = getmin(a, b, 2*k+2, (l+r)/2, r);
        return min(vl, vr);
    }
};

//遅延セグ木
struct LazySegmentTree {
private:
    int n;
    vector<int> node, lazy;
    vector<bool> lazyFlag;

public:
    LazySegmentTree(vector<int> v) {
        int sz = (int)v.size();
        n = 1; while(n < sz) n *= 2;
        node.resize(2*n-1);
        lazy.resize(2*n-1, inf);
        lazyFlag.resize(2*n-1, false);

        for(int i=0; i<sz; i++) node[i+n-1] = v[i];
        for(int i=n-2; i>=0; i--) node[i] = min(node[i*2+1], node[i*2+2]);
    }

    void lazyEvaluate(int k, int l, int r) {
        if(lazyFlag[k]) {
            node[k] = lazy[k];
            if(r - l > 1) {
                lazy[k*2+1] = lazy[k*2+2] = lazy[k];
                lazyFlag[k*2+1] = lazyFlag[k*2+2] = true;
            }
            lazyFlag[k] = false;
        }
    }

    void update(int a, int b, int x, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        lazyEvaluate(k, l, r);
        if(b <= l || r <= a) return;
        if(a <= l && r <= b) {
            lazy[k] = x;
            lazyFlag[k] = true;
            lazyEvaluate(k, l, r);
        }
        else {
            update(a, b, x, 2*k+1, l, (l+r)/2);
            update(a, b, x, 2*k+2, (l+r)/2, r);
            node[k] = min(node[2*k+1], node[2*k+2]);
        }
    }

    int find(int a, int b, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        lazyEvaluate(k, l, r);
        if(b <= l || r <= a) return inf;
        if(a <= l && r <= b) return node[k];
        int vl = find(a, b, 2*k+1, l, (l+r)/2);
        int vr = find(a, b, 2*k+2, (l+r)/2, r);
        return min(vl, vr);
    }
};
*/


/********変数宣言********/
//vector<long long> g[200020];
vector<pair<long long,long long>> g[200020];
ll s[200020];
bool used[200020];
//bool dp[100005];

ll A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,Q,R,S,T,U,V,W,X,Y,Z;
double dA,dB,dC,dD,dE,dF,dG,dH,dI,dJ,dK,dL,dM,dN,dO,dP,dQ,dR,dS,dT,dU,dV,dW,dX,dY,dZ;


string sa,sb,sc,sd,se,sf,sg,sh,si,sj,sk,sl,sm,sn,so,sp,sq,sr,ss, su,sv,sw,sx,sy,sz;

//1000000000000000000  //10^18
//1000000000           //10^9

//ABCDEFGHIJKLMNOPQRSTUVWXYZ    //26


//using lll=__int128_t;

int main()
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	/********よく使う********/

	
	/*マップ*/
	//map<ll, ll, std::greater<ll>> mp;

	/*デキュー*/
	//deque<long long> dque;

	/*文字列*/
	//string s;
	//wk=(ll)stoi(s);
	//wk=stoll(s);
	//t-'a'+'A'//大文字化
	//string t;
	//t=s.substr(0,1);//0文字目から1つ取り出す
	//if(s.size()%2==0 && s.substr(0,s.size()/2)==s.substr((s.size())/2))//引数一つの時はその個所から最後まで
	//s.insert(0, " ");
	//reverse(s.begin(),s.end());
	//s+="-AI";
	//s+=char('a'+N%26);
	//string t;
	//t=s.substr(s.size()-2);
	//to_bigger(t);//返り値無し 文字列を大文字化
	//cout << s.substr(0,s.size()-2)+t << "\n";
	
	/*セット*/
	//set<ll> st;
	
	/*スタック*/
	/*
	stack<char>sta;
	rep(i,t.size()){
		if(sta.empty()){
			sta.push(t[i]);
		}
		else{
			if(sta.top()==t[i]){
				sta.pop();
			}
			else{
				sta.push(t[i]);
			}
		}
	}

	vector<char>v(sta.size());
	ll i=0;
	while(!sta.empty()){
		v[i]=sta.top();
		sta.pop();
		i++;
	}
	rep(i,v.size()){
		pr("%c",v[v.size()-i-1]);
	}
	*/
	/*キュー*/
	//queue<long long> que;

	
	/*パミュ*/
	//do{
	//}while(next_permutation(v.begin(),v.end()));

	/*でかい数*/
	//__int128  aa = 1;
	//lll p=1;

	/*エラトステネスの篩*/
	//wk=sieve(p);

	/*pow_mod*/
	//powmod(10, n, m * m) 
	/******初期化***********/

	long long ans,ans1,ans2,ans3,ans4;
	long long sum,sum1,sum2,sum3,sum4;
	long long cnt,cnt1,cnt2,cnt3,cnt4;
	long long flg,flg1,flg2,flg3,flg4;
	long long wk,wk1,wk2,wk3,wk4;
	
	long long max,max1,max2,max3,max4;
	long long min,min1,min2,min3,min4;
	ans=ans1=ans2=ans3=ans4=0;
	sum=sum1=sum2=sum3=sum4=0;
	cnt=cnt1=cnt2=cnt3=cnt4=0;
	flg=flg1=flg2=flg3=flg4=0;
	wk=wk1=wk2=wk3=wk4=0;
	
	max=max1=max2=max3=max4=0;
	min=min1=min2=min3=min4=INF;

	double dwk,dwk1,dwk2,dwk3,dwk4;
	double dsum,dsum1,dsum2,dsum3,dsum4;
	double dans,dans1,dans2,dans3,dans4;
	dwk=dwk1=dwk2=dwk3=dwk4=0;
	dsum=dsum1=dsum2=dsum3=dsum4=0;
	dans=dans1=dans2=dans3=dans4=0;
	string s;
	cin>>s;
	rep(i,s.size()){
		if(s[i]=='a'){
			cnt++;
			max=MAX(max,cnt);
		}
		else{
		}
	}
	rep(i,max+1){
		cout<<"a";
	}
	cout<<"\n";
	// 前処理
    //COMinit();

    // 計算例
    //cout << COM(100000, 50000) << endl;
	/*ベクター*/
	//std::sort(v.begin(),v.end());//昇順ソート
	//sort(all(v));
	//std::sort(v.begin(),v.end(),std::greater<long long>());//降順ソート
	//v.erase(unique(v.begin(), v.end()), v.end());
	//vector<ll> v(N, 0);

	/*ペア*/
	//vector<pair<long long, long long> > p(N);
	//sort(p.begin(), p.end());
	//sort(p.begin(), p.end(),greater<pair<long long,long long> >());
	//vector<P>w;
	//w.push_back({wk1,wk2});

	/*プライオリティキュー*/
	//priority_queue<lon long, vector<long long>, greater<long long> > que;
	//priority_queue<long long> que;

	/*
	cin >> N;
	vector<ll>v(N);
	rep(i,N){
		cin >> v[i];
	}
	*/

	/******出力関連***********/
	//pr("%lld\n",N);
	//printf("%lld",(ll)ceil(dB/dA));
	//puts("Yes");
	//文字列の出力
	//std::cout << s << std::endl;
	//printf("%.12f\n",ret);
	//cout << sum << '\n';
	//pr("%02lld:%02lld",wk/60,wk%60);

	/******CF***********/
	/*
	cin >> T;
	while(T--){
		cin >> N >> K;
		std::vector<long long> v(N);	
		// 配列入力1
		
		for(long long i=0; i<N; i++){
			std::cin >> v[i];
		}
		
		//std::sort(v.begin(),v.end(),std::greater<long long>());//降順ソート
		//cout << sum << '\n';
		//文字列の出力
    	//std::cout << s << std::endl;
		
		//ラベル
		//goto end;
		//end:
		
	}*/
	//re 0;

	/******よく使う***********/

	//素因数分解
	//1の場合pfは空 5の場合pfはfi=5,se=1
	/*
	auto pf = prime_factorize(v[i]);
	for(auto p:pf){
		if(p.se!=wk){		
		}
	}
	*/
	//約数列挙
	/*
	vector<long long> div = calc_divisor(M);

	// M の約数 d であって、d * N <= M となる最大の d を求める
	long long res = 1;
	for (auto d : div) {
		if (d * N <= M) res = max(res, d);
	}
	*/

	//最小公倍数
	/*
	std::vector<ll> v(N);
	rep(i, N) {
		cin >> v[i];
	}	
	cout << lcm(v) << endl;
	return 0;
	*/

	//最小公約数
	/*
	std::vector<ll> v(N);
	rep(i, N) {
		cin >> v[i];
	}	
	cout << gcd(v) << endl;
	return 0;
	*/

	//素数判定
	/*
	for(int i=x; ; i++){
		bool dame=0;
		for(int j=2; j*j<=i; j++){
			if(i%j==0){
				dame=1;
				break;
			}
		}
		if(!dame){
			cout<<i<<endl;
			return 0;
		}
	}
	*/
	//set典型
	/*
	std::set<long long> st;
	for(long long i=0; i<N; i++){
		std::cin >> v[i];
		if(st.find(v[i])==st.end()){
			st.insert(v[i]);
		}
		else{
			st.erase(v[i]);
		}
	}
	//set典型2
	rep(i,N){
		max=MAX(max,v[i]);
		min=MIN(min,v[i]);
	}
	std::set<long long> st;
	for(long long i=0; i<N; i++){
		if(st.find(v[i])==st.end()){
			st.insert(v[i]);
		}
		else{
			//st.erase(v[i]);
		}
	}
	while(max-min!=0){
		st.erase(max);
		if(st.find(max-min)==st.end()){
			st.insert(max-min);
		}
		max=*st.rbegin();//最小
		min=*st.begin();//最大
	}
	for(auto itr = st.begin(); itr != st.end(); ++itr) {
		std::cout << *itr << " ";      // イテレータの指す先のデータを表示
	}

	//map典型
	int minv = mp.begin()->first;//最小
	int maxv = mp.rbegin()->first;//最大
	
	//stack典型

	stack<char> sta;   

	rep(i,s.size()){
		if(s[i]=='A'){
			sta.push('A');
		}
		else{
			if(sta.empty()){
				sta.push('B');
			}
			else if(sta.top()=='B'){
				sta.pop();
			}
			else{
				sta.pop();
			}
		}
	}
	cout<<sta.size()<<"\n";

	//整数判定
	//if(ceil(sqrt(wk)==floor(sqrt(wk))))

	//パミュ
	/*
	sort(v.begin(),v.end());
	do{
	}while(next_permutation(v.begin(),v.end()));
	*/

	//26進数
	/*
	string s;
	while(N>=0){
		s+=char('a'+N%26);
		N/=26;
		N--;
	}
	reverse(all(s));
	*/
	//N進数からK進数へ
	/*
	string s;
	s=Itoa(N,K);
	pr("%lld",(ll)s.size());
	//putchar('\n');
	re 0;
	*/

	/******出力関連***********/
	//pr("%lld\n",N);
	//printf("%lld",(ll)ceil(dB/dA));
	//puts("Yes");
	//文字列の出力
	//std::cout << s << std::endl;
	//printf("%.12f\n",ret);
	//cout << sum << '\n';
	//pr("%02lld:%02lld",wk/60,wk%60);

	re 0;
    
}