#include<bits/stdc++.h>
#define Gc() getchar()
#define Me(x,y) memset(x,y,sizeof(x))
#define Mc(x,y) memcpy(x,y,sizeof(x))
#define d(x,y) ((m)*(x-1)+(y))
#define R(n) (rnd()%(n)+1)
#define Pc(x) putchar(x)
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define eb emplace_back
#define all(x) x.begin(),x.end()
using namespace std;using ll=long long;using db=double;using lb=long db;using ui=unsigned;using ull=unsigned long long;using pii=pair<int,int>;
const int N=1.5e5+5,M=100+5,K=1000+5,mod=1e9+7,Mod=mod-1;const db eps=1e-9;const int INF=1e9+7;mt19937 rnd(time(0));
#define Tp template<typename T>
#define Ts template<typename T,typename... Ar>
namespace Debug{
	Tp void _debug(char* f,T t){cerr<<f<<'='<<t<<endl;}
	Ts void _debug(char* f,T x,Ar... y){while(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
	#ifdef LOCAL
	#define gdb(...) _debug((char*)#__VA_ARGS__,__VA_ARGS__)
	#else 
	#define gdb(...) void()
	#endif
}using namespace Debug;
int n,m;char s[N];
int pre[41][N],lp[41][N],suf[41][N],ls[41][N];
void work(){
	for(int i=1;i<=n;i++){
		pre[0][i]=(s[i]=='b'),lp[0][i]=1,pre[1][i]=(s[i]=='a'),lp[1][i]=1;
	}
	for(int i=2;i<=40;i++){
		for(int j=1;j<=n;j++){
			pre[i][j]=pre[i-2][j]+pre[i-1][j-pre[i-2][j]];
			lp[i][j]=lp[i-2][j]+lp[i-1][j-pre[i-2][j]];
		}
	}
	for(int i=1;i<=n;i++){
		suf[0][i]=(s[i]=='b');ls[0][i]=1;suf[1][i]=(s[i]=='a');ls[1][i]=1;
	}
	for(int i=2;i<=40;i++){
		for(int j=1;j<=n;j++){
			suf[i][j]=suf[i-1][j]+suf[i-2][j+suf[i-1][j]];
			ls[i][j]=ls[i-1][j]+ls[i-2][j+suf[i-1][j]];
		}
	}
}
void Solve(){
	int i,j;scanf("%s",s+1);n=strlen(s+1);
	work();
	int ans=INF;
	for(int i=2;i<=40;i++) for(int j=0;j<=n;j++) if(pre[i-1][j]>=j&&suf[i-2][j+1]>=n-j) ans=min(ans,lp[i-1][j]+ls[i-2][j+1]);
	printf("%d\n",ans);
}
int main(){
	int t=1;
	// scanf("%d",&t);
	while(t--) Solve();
	cerr<<clock()*1.0/CLOCKS_PER_SEC<<'\n';
}