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

#define ll long long
#define elif else if

#define repname(a, b, c, d, e, ...) e
#define rep(...)                    repname(__VA_ARGS__, rep3, rep2, rep1, rep0)(__VA_ARGS__)
#define rep0(x)                     for (int rep_counter = 0; rep_counter < (x); ++rep_counter)
#define rep1(i, x)                  for (int i = 0; i < (x); ++i)
#define rep2(i, l, r)               for (int i = (l); i < (r); ++i)
#define rep3(i, l, r, c)            for (int i = (l); i < (r); i += (c))

struct ScalarInput {
    template<class T>
    operator T(){
        T ret;
        cin >> ret;
        return ret;
    }
};
struct VectorInput {
    size_t n;
    VectorInput(size_t n): n(n) {}
    template<class T>
    operator vector<T>(){
        vector<T> ret(n);
        for(T &x : ret) cin >> x;
        return ret;
    }
};
ScalarInput input(){ return ScalarInput(); }
VectorInput input(size_t n){ return VectorInput(n); }

template<typename T>
void print(vector<T> a){
  for(int i=0;i<a.size();i++){
    cout<<a[i]<<" \n"[i+1==a.size()];
  }
}

template<class T>
void print(T x){
    cout << x << '\n';
}
 
template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail){
  cout << head << ' ';
  print(forward<Tail>(tail)...);
}

// change min, change max
template<class T>
bool chmin(T &a, const T &b) {if (a > b) {a = b; return 1;} return 0;}
template<class T>
bool chmax(T &a, const T &b) {if (a < b) {a = b; return 1;} return 0;}


string T;
int n;
vector<vector<pair<bool,int>>>Pre(50),Suf(50);
vector<int>sz(50);
int ans;

bool dbg=false;

void calc(int i){
  if(Pre[i].size()!=0)return;
  Pre[i]=vector<pair<bool,int>>(n);
  Suf[i]=vector<pair<bool,int>>(n);
  if(i==0){
    rep(j,n){
      if(T[j]=='b'){
        Pre[i][j]={false,j+1};
        Suf[i][j]={false,j-1};
        if(j==n-1){
          Pre[i][j]={true,1};
        }
        if(j==0){
          Suf[i][j]={true,1};
        }
      }
      else{
        Pre[i][j]={false,j};
        Suf[i][j]={false,j};
      }
    }
    sz[i]=1;
  }
  elif(i==1){
    rep(j,n){
      if(T[j]=='a'){
        Pre[i][j]={false,j+1};
        Suf[i][j]={false,j-1};
        if(j==n-1){
          Pre[i][j]={true,1};
        }
        if(j==0){
          Suf[i][j]={true,1};
        }
      }
      else{
        Pre[i][j]={false,j};
        Suf[i][j]={false,j};
      }
    }
    sz[i]=1;
  }
  else{
    calc(i-2);
    calc(i-1);
    sz[i]=sz[i-1]+sz[i-2];
    rep(j,1,n){
      if(Suf[i-1][j-1].first&&Pre[i-2][j].first){
        ans=min(ans,Suf[i-1][j-1].second+Pre[i-2][j].second);
      };
    }
    rep(j,n){
      if(Pre[i-1][j].first)Pre[i][j]=Pre[i-1][j];
      else{
        int k=Pre[i-1][j].second;
        if(Pre[i-2][k].first){
          Pre[i][j]={true,sz[i-1]+Pre[i-2][k].second};
        }
        else{
          Pre[i][j]=Pre[i-2][k];
        }
      }
      if(Suf[i-2][j].first)Suf[i][j]=Suf[i-2][j];
      else{
        int k=Suf[i-2][j].second;
        if(Suf[i-1][k].first){
          Suf[i][j]={true,sz[i-2]+Suf[i-1][k].second};
        }
        else{
          Suf[i][j]=Suf[i-1][k];
        }
      }
    }
    if(Suf[i][n-1].first)ans=min(ans,Suf[i][n-1].second);
    if(Pre[i][0].first)ans=min(ans,Pre[i][0].second);
  }
  if(dbg){
    vector<int>ok,res;
    rep(j,n){
      if(Pre[i][j].first)ok.push_back(1);
      else ok.push_back(0);
      res.push_back(Pre[i][j].second);
    }
    print("Pre",i);
    print(ok);
    print(res);
  }
  return;
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cin>>T;
  n=T.size();
  if(n==1){
    print(1);
    exit(0);
  }
  ans=1<<30;
  if(dbg)calc(8);
  else calc(30);
  print(ans);
}