#include <bits/stdc++.h>

using namespace std;

int main()
{
    string s;
    cin >> s;

    map<char, vector<int>> db;
    string betuk = "ACGT";
    for(auto x : betuk){
        db[x] = vector<int>(s.size()+1, 0);
    }
    for(int i = 1; i <= s.size(); i++){
        for(auto x : betuk){
            db[x][i] = db[x][i-1];
        }
        db[s[i-1]][i]++;
    }

    int mo = 0;
    int l = 0;
    int r = s.size();
    int mid;
    while(l <= r){
        mid = (l+r) / 2;
        bool lehet = false;
        for(int i = 1; i <= s.size() - mid + 1; i++){
            int legtobb = 0;
            for(auto x : betuk){
                legtobb = max(legtobb, db[x][i+mid-1] - db[x][i-1]);
            }
            if(legtobb*2 >= mid){
                lehet = true;
                break;
            }
        }
        if(lehet){
            mo = mid;
            l = mid+1;
        }
        else{
            r = mid-1;
        }
    }
    cout << mo << "\n";
}