#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic pop
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  string s;
  cin >> s;
  int ans = 0;
  rep(i, n - 1) if (s[i] == 'B' && s[i+1] == 'B') ans = 1;
  for(int i = 0; i < n;) {
    if (s[i] == 'B') {
      i++;
      continue;
    }
    int j = i + 1;
    while(j < n && s[j] == 'A') j++;
    if (i == 0) {
      if (j == n) {
        ans += j - i - 1;
      } else {
        ans += j - i;
      }
    } else {
      if (j == n) {
        ans += j - i;
      } else {
        if (j - i == 1) ans++;
        else ans += j - i + 1;
      }
    }
    i = j;
  }
  cout << ans << '\n';
}