//
//
//  Codeforces: ganariya
//  AtCoder: ganariya2525
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//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <complex>
#include <regex>
#include <locale>
#include <random>
#include <type_traits>

using namespace std;

#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v){std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}

using LL = long long;

//~~~~~~~~~~~~~~~~~~~~~_(＾～＾ ｣ ∠)_~~~~~~~~~~~~~~~~~~~~~

const string AGCT = "AGCT";

int main() {

    string S;
    cin >> S;

    int N = S.size();

    vector<int> a(N, 0);
    for (int i = 0; i < N; i++) for (int j = 0; j < 4; j++) if (S[i] == AGCT[j]) a[i] = 1;

    int ans = 0;
    for (int i = 0, j = 0; j < N; i = j) {
        while (j < N && a[i] == a[j])j++;
        if (a[i] == 1) ans = max(ans, j - i);
    }

    cout << ans;

    return 0;
}










































Measured memory_bytes: 256