// UUID: 6462593f-518e-4e3b-af12-629989d3c95c
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
#define pii pair<int, int>
#define pb push_back
#define srt(x) x.begin(),x.end()
const int INF = 1e9 + 7;

int ans = 1, n;
string s;

void calc(char c)
{
    int curr = 0;
    vector<int>m(n+2, -1);
    for(int i = 0; i < n; i++) 
    {
        curr += (s[i] == c ? 1 : -1);
        if(curr >= 0)
        {
            ans = max(ans, i);
            continue;
        }
        if(m[-curr] >= 0) ans = max(ans, i - m[-curr]);
        else m[-curr] = i;
    }
}

signed main() {
    ios::sync_with_stdio(false);cin.tie(nullptr);
    cin >> s;
    n = s.size();
    calc('A');
    calc('C');
    calc('G');
    calc('T');
    cout << ans;
}