// UUID: 224ad4d1-ffc5-41ec-8e35-bb9c5ca739ec
#include <bits/stdc++.h>
using namespace std;

string s;
int ans = 0;

void solve(char c) {
    int curr = 0, n = s.size();
    vector<int> occ = {-1};
    for (int i = 0; i < n; i++) {
        if (s[i] == c) curr++;
        else curr--;
        if (-curr == occ.size()) occ.push_back(i);
        int idk = -min(0, curr);
        ans = max(ans, i - occ[idk]);
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    cin >> s;
    solve('A');
    solve('C');
    solve('G');
    solve('T');
    cout << ans;
    return 0;
}