#include using namespace std; #define int long long #define rep(i,l,r) for(int i=(int)(l);i<(int)(r);i++) #define all(x) (x).begin(),(x).end() #define pb push_back templatebool chmax(T &a,T b){if(abool chmin(T &a,T b){if(a>b){a=b;return 1;}return 0;} typedef pair pii; typedef vector vi; typedef vector vvi; const int inf = 1LL<<60; const int mod = 1e9 + 7; const double eps = 1e-9; /*{ }*/ signed main() { string s; cin >> s; int n = s.size(); map m; int cnt = 0, ans = 0; rep(i, 0, n){ if(s[i] == 'A'){ cnt++; }else{ cnt--; } if(m.count(cnt) > 0){ chmax(ans, i-m[cnt]); }else{ m[cnt] = i; } } cout << ans << endl; return 0; }