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

int bs(const vector<int> &v, int a) {
	int l = 0, r = (int)v.size();
	while (l < r) {
		int m = (l + r) / 2;
		if (v[m] < a)
			l = m + 1;
		else
			r = m;
	}
	return l;
}

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

	int n;
	cin >> n;
	string S;
	cin >> S;

	int ct[3] = {0, 0, 0};
	vector<int> P[3];
	for (int i = 0; i < n; ++i)
		P[S[i]-'A'].push_back(i),
		P[S[i]-'A'].push_back(i+n),
		ct[S[i]-'A']++;
	sort(P[0].begin(), P[0].end());
	sort(P[1].begin(), P[1].end());
	sort(P[2].begin(), P[2].end());

	int a = 0;
	for (int i = 0; i < n; ++i)
		a = max(a, max(
			bs(P[0], i+ct[0])
				- bs(P[0], i)
			+ bs(P[1], i+ct[0]+ct[1])
				- bs(P[1], i+ct[0])
			+ bs(P[2], i+ct[0]+ct[1]+ct[2])
				- bs(P[2], i+ct[0]+ct[1]),
			bs(P[0], i+ct[0])
				- bs(P[0], i)
			+ bs(P[2], i+ct[0]+ct[2])
				- bs(P[2], i+ct[0])
			+ bs(P[1], i+ct[0]+ct[2]+ct[1])
				- bs(P[1], i+ct[0]+ct[2])
					));

	cout << n-a << endl;

	return 0;
}