#include <bits/stdc++.h>
using namespace std;

int n;
string s;

int solve(char c){
    int ans=0,cnt=0;
    vector<int> first(2*n+2,-1);
    for(int i=0;i<n;i++){
        char ch=s[i];
        if(ch==c)cnt++;else cnt--;
        if(first[cnt+n]==-1){
            first[cnt+n]=i;
        }else{
            ans=max(ans,i-first[cnt+n]);
        }
    }
    if(cnt>=0)return n;
    return ans;
}

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