#include<bits/stdc++.h>
using namespace std;
#include <unordered_set>
#include <random>
//#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=MOD;
const ll MAX=200010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;

ll dx[]={0,1,0,-1};
ll dy[]={1,0,-1,0};



void solve(){
    ll n;cin>>n;
    string s;cin>>s;
    string mm="ATGC";
    vector<ll>m(4);
    rep(i,4)m[i]=mm[i]-'A';
    vector<ll>cnt(26);

    rep(i,n){
        cnt[s[i]-'A']++;
    }
    ll now=0;
    ll ans=0;
    rep(i,n){
        string t=s;
        ll c1=0;
        rep(k,4){
            c1+=cnt[(m[k]+26-now)%26];
        }
        if(c1==0)break;
        ans++;
        c1--;
        cnt[s[c1]-'A']--;
        ll c2=cnt[s[c1]-'A'];
        s.erase(c1,1);
        now+=c2;
        now%=26;
    }
    cout<<ans<<endl;
}

signed main(){
    //cin.tie(0);
    //ios::sync_with_stdio(false);
    solve();
}