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

int main()
{
	int N;
	string S;
	cin >> N >> S;
	
	int cnt = 0;
	queue<char> q;
	for(int i = 0; i < N; i++) if(S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T') cnt++;
	if(cnt == 0)
	{
		cout << 0 << endl;
		return 0;
	}
	
	int ans = 0;
	for(int i = 0; i < N; i++)
	{
		q.push(S[i]);
		while((int)q.size() == cnt)
		{
			ans++;
			if(q.front() == 'A' || q.front() == 'G' || q.front() == 'C' || q.front() == 'T') cnt--;
			if(cnt == 0)
			{
				cout << ans << endl;
				return 0;
			}
			q.pop();
		}
	}
	return 0;
}