// UUID: a7f5f562-e2f1-4d26-ad1d-a20d6308bb2c
#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    string s; cin >> s;
    int n = s.size();

    int ans = 0;
    string l = "ACGT";

    for (char ch : l) {
        int pr = 0;
        int off = n + 5;
        vector<int> v(2 * n + 10, -1);

        v[off] = 0;

        for (int i = 0; i < n; i++) {
            if (s[i] == ch) pr++;
            else pr--;
            int idx = pr + off;
            if (v[idx] == -1)v[idx] = i + 1;
            if (pr >= 0)ans = max(ans, i + 1);
            else ans = max(ans, i + 1 - v[idx]);
        }
    }

    cout << ans << "\n";
    return 0;
}