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

#define rep(i, n) for(ll i = 0; i < n; i++)
#define rep2(i, m, n) for(ll i = m; i <= n; i++)
#define rrep(i, m, n) for(ll i = m; i >= n; i--)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define MAX(x) *max_element(all(x))
#define MIN(x) *min_element(all(x))
#define SZ(a) ((ll)(a).size())
#define bit(n, k) ((n >> k) & 1)
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
const int dx[4] = { -1, 1, 0, 0 };
const int dy[4] = { 0, 0, 1, -1 };
const int inf = 1e9 + 1;
const ll INF = 1e18;
const double pi = acos(-1);

using Graph = vector<vector<ll>>;
using REV_PQ = priority_queue<ll, vector<ll>, greater<ll>>;
using PQ = priority_queue<ll>;

//typedef atcoder::modint998244353 mint;
//typedef atcoder::modint1000000007 mint;

const int SIZE = 200010;
ll powll(ll n, ll x) {
    // return n ^ x;

    ll ret = 1;
    rep(i, x) ret *= n;

    return ret;
}

/*struct Edge { ll u, v, cost; };

bool comp(const Edge& e1, const Edge& e2) {
    return e1.cost < e2.cost;
}*/


void OutputYesNo(bool val) {

    if (val) cout << "Yes" << endl;
    else cout << "No" << endl;
}
void OutputTakahashiAoki(bool val) {

    if (val) cout << "Takahashi" << endl;
    else cout << "Aoki" << endl;
}

void OutPutInteger(ll x) { cout << x << endl; }
void OutPutString(string x) { cout << x << endl; }
/*

int t; cin >> t;
rep2(i, 1, t){
    cout << "Case #" << i << ":" << endl;
    cout << "Case #" << x << ":" << " ";
}
*/


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);


    int n; cin >> n;
    string s; cin >> s;

    int sc = 0;
    vector<char> c = { 'A', 'G', 'C', 'T' };

    int res = 0;
    rep(i, n)rep(j, 4) if (s[i] == c[j]) res = i + 1;


    OutPutInteger(res);

}