#include <bits/stdc++.h>
#define be(v) (v).begin(),(v).end()
#define pb(q) push_back(q)
#define rep(i, n) for(int i=0;i<n;i++)
#define all(i, v) for(auto& i : v)
typedef long long ll;
using namespace std;
const ll mod=1000000007, INF=(1LL<<60);
#define doublecout(a) cout<<fixed<<setprecision(10)<<a<<endl;


/////////segmenttree
struct SegmentTree {
private:
    ll n;
    vector<ll> node;
    ll ID = 0; // min -> INF, max, sum -> 0
    inline ll func(ll a, ll b){return a + b;} /////////

public:
    SegmentTree(vector<ll> v) {
        int sz = v.size();
        n = 1; while(n < sz) n *= 2;
        node.resize(2*n-1, ID);
        for(int i=0; i<sz; i++) node[i+n-1] = v[i];
        for(int i=n-2; i>=0; i--) node[i] = func(node[2*i+1], node[2*i+2]);
    }

    void update(ll x, ll val) {
        x += (n - 1);
        node[x] = val;
        while(x > 0) {
            x = (x - 1) / 2;
            node[x] = func(node[2*x+1], node[2*x+2]);
        }
    }

    ll get(ll a, ll b, ll k=0, ll l=0, ll r=-1) {
        if(r < 0) r = n;
        if(r <= a || b <= l) return ID;
        if(a <= l && r <= b) return node[k];

        ll vl = get(a, b, 2*k+1, l, (l+r)/2);
        ll vr = get(a, b, 2*k+2, (l+r)/2, r);
        return func(vl, vr);
    }
};


int ss(ll a, ll p) {
    a %= p;
    a += p;
    a %= p;
    return a;
}
int main() {
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    SegmentTree seg(vector<ll> (n, 1));
    int count = 0;
    string t = "AGCT";
    string s;
    cin >> s;
    vector<ll> cnt(26, 0);
    rep(i, n) {
        rep(j, 4) if(s[i] == t[j]) count++;
        cnt[s[i] - 'A']++;
    }
    if(count == 0) {
        cout << 0 << endl;
        return 0;
    }
    seg.update(count - 1, 0);
    ll num = --cnt[s[count - 1] - 'A'];
    vector<ll> nx(26);
    ll flip = num;
    rep(i, 26) {
        nx[(i + num) % 26] = cnt[i];
    }
    swap(nx, cnt);

    while(1) {
        ll cc = 0;
        rep(i, 4) {
            cc += cnt[ss(ll(t[i] - 'A') - flip, 26)];
        }
        if(!cc) break;
        ll le = 0, ri = cc;
        while(ri - le > 1) {
            ll mid = (ri + le ) / 2;
            if(seg.get(0, mid) >= cc) ri = mid;
            else le = mid;
        }
        seg.update(ri - 1, 0);
        num = --cnt[s[ri - 1] - 'A'];
        flip += num;
        rep(i, 26) {
            nx[(i + num) % 26] = cnt[i];
        }
        swap(nx, cnt);
    }
    cout << n - seg.get(0, n) << endl;
    return 0;
}