// Source: https://usaco.guide/general/io

#include <bits/stdc++.h>
using namespace std;
int n;
string s;
int tolt(char c)
{
int ans=0;
int sum=0;
vector<int> a(2*n+5,-1);
for(int i=0;i<n;i++)
    {
    if(s[i]==c)sum++;
    else sum--;
    if(a[sum+n]==-1)
        {
        a[sum+n]=i;
        //ans=max(ans,i-a[sum+n]);
        }
    else ans=max(ans,i-a[sum+n]);
    }
if(sum>=0)return n;
return ans;
}

int main() {
    cin>>s;
    n=s.size();
    cout<<max(tolt('A'),max(tolt('C'),max(tolt('G'),tolt('T'))));
}