#include <bits/stdc++.h>

using namespace std;

// megadott hivatalos megoldás

int main()
{
    const char acgt[4] = {'A', 'C', 'G', 'T'};

    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie();

    string dns; cin >> dns;
    int n = dns.length();
    int ans = 0;

    for (char c : acgt)
    {
        vector<int> first_occur(n + 1, -1);
        int cnt = 0;
        for (int i = 0; i < n; ++i)
        {
            cnt += dns[i] == c ? 1 : -1;
            if (cnt >= 0)
                ans = max(ans, i + 1);
            else
            {
                if (first_occur[-cnt] == -1)
                    first_occur[-cnt] = i;
                else
                    ans = max(ans, i - first_occur[-cnt]);
            }
        }
    }

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