#include<bits/stdc++.h>
using namespace std;
const int N=1e5+2;
int n,ans=INT_MAX;
struct node{
	int len;
	pair<int,int>f[N],g[N];
}a,b;
node merge(node&x,node&y){
	node z;
	z.len=x.len+y.len;
	for(int i=1;i<=n;i++){
		z.f[i]=x.f[i].first==n+1?x.f[i]:make_pair(y.f[x.f[i].first].first,x.len+y.f[x.f[i].first].second),
		z.g[i]=y.g[i].first== 0 ?y.g[i]:make_pair(x.g[y.g[i].first].first,y.len+x.g[y.g[i].first].second);
		if(x.g[i].first==0&&y.f[i+1].first==n+1)ans=min(ans,x.g[i].second+y.f[i+1].second);
	}
	return z;
}
string s;
signed main(){
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	cin>>s,n=s.size();
	for(int i=1;i<=n;i++)if(s[i-1]=='a')b.f[i]={i+1,1},b.g[i]={i-1,1},a.f[i]=a.g[i]={i,0};
		else a.f[i]={i+1,1},a.g[i]={i-1,1},b.f[i]=b.g[i]={i,0};
	a.len=b.len=1;
	for(int i=1;i<=30;i++)swap(a,b),b=merge(a,b); 
	cout<<ans;
}