#include "bits/stdc++.h" using namespace std; #define DEBUG(x) cout<<#x<<": "<<x<<endl; #define DEBUG_VEC(v) cout<<#v<<":";for(int i=0;i<v.size();i++) cout<<" "<<v[i]; cout<<endl typedef long long ll; #define vi vector<int> #define vl vector<ll> #define vii vector< vector<int> > #define vll vector< vector<ll> > #define vs vector<string> #define pii pair<int,int> #define pis pair<int,string> #define psi pair<string,int> #define pll pair<ll,ll> #define fi first #define se second #define rep(i,n) for(int i=0;i<(int)(n);i++) #define rep1(i,n) for(int i=1;i<=(int)(n);i++) #define all(c) c.begin(),c.end() const int inf = 1000000001; const ll INF = 2e18; const ll MOD = 1000000007; //const ll mod = 1000000009; const double pi = 3.14159265358979323846; #define Sp(p) cout<<setprecision(15)<< fixed<<p;//<<endl; int dx[4] = { 1,0, -1,0 }, dy[4] = { 0,1,0,-1 }; int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 }; int main() { string s; cin >> s; int n = s.size(); vi a(n + 1); int cnt = 0; int mi = inf, ma = -inf; rep(i, n) { if (s[i] == 'A') { cnt++; } else { cnt--; } a[i + 1] = cnt; mi = min(mi, cnt); ma = max(ma, cnt); } int ans = 0; for (int i = n; i >= 0; i--) { if (a[i] == 0) { ans = i; break; } } map<int, int> l, r; rep(i, n + 1) { if (l[a[i]] == 0) { l[a[i]] = i; } } for (int i = n; i >= 0; i--) { if (r[a[i]] == 0) { r[a[i]] = i; } } for (int x = mi; x <= ma; x++) { if (x == 0) { continue; } ans = max(r[x] - l[x], ans); } cout << ans << endl; }