#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <array>
#include <atcoder/modint>
#include <atcoder/segtree>
using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(int)(n); i++)

const i64 INF = 1001001001001001001;

using modint = atcoder::static_modint<998244353>;

namespace RQ{
    using S = int;
    S op(S l, S r){ return l+r; }
    S e(){ return 0; }
    struct LessThan{
        int a;
        bool operator()(S x) const { return x < a; }
    };
    using RQ = atcoder::segtree<S,op,e>;
}


int main(){
    int N; cin >> N;
    string S; cin >> S;
    int cnt[26] = {};
    rep(i,N) cnt[S[i]-'A']++;
    int slide = 0;

    RQ::RQ F(vector<RQ::S>(N, 1));

    auto reverse_slide = [&](int x) -> int { return (x + 26 - slide % 26) % 26; };

    int ans = 0;
    while(true){
        int c1 = cnt[reverse_slide('A'-'A')] + cnt[reverse_slide('T'-'A')] + cnt[reverse_slide('G'-'A')] + cnt[reverse_slide('C'-'A')];
        if(c1 == 0) break;
        ans++;
        int c1th = F.max_right(0, RQ::LessThan{c1});
        int ch = S[c1th]-'A';
        cnt[ch]--;
        F.set(c1th, 0);
        slide += cnt[ch];
        slide %= 26;
    }

    cout << ans << endl;
    return 0;
}


struct ios_do_not_sync{
    ios_do_not_sync(){
        std::ios::sync_with_stdio(false);
        std::cin.tie(nullptr);
    }
} ios_do_not_sync_instance;