#include <bits/stdc++.h>
using namespace std;
const int c = 2e5;
int main() {
    string s; cin >> s;
    vector<char> ps = {'A','C','G','T'};
    vector<int> pr(c+1,c);
    int out = 0;
    for (int i = 0; i < 4; i++) {
        int cnt = 0;
        for (int j = 0; j < s.size(); j++) {
            if (s[j] == ps[i]) cnt++;
            else cnt--;
            out = max(out,j-pr[c+cnt]);
            pr[cnt+c] = min(pr[cnt+c],j);
        }
    }
    cout << out << '\n';
}