#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <utility>
#include <tuple>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <cctype>
#include <cassert>
#include <functional>
#include <numeric>
#include <type_traits>
using namespace std;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define coutf(f) cout << fixed << setprecision(f)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

int main() {
	int n;
	string s;
	cin >> n >> s;
	int ans = n - 1, base = 0;
	rep(i, n - 1) {
		if (s[i] == 'B' && s[i + 1] == 'B') {
			ans--;
			base = 1;
		}
	}
	rep(i, n - 2) {
		if (s[i] == 'B' && s[i + 1] == 'A' && s[i + 2] == 'B') ans--;
	}
	ans += base;
	cout << ans << endl;
	return 0;
}