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

#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
#define x first
#define y second
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)

typedef long long ll;
typedef double db;
typedef long double LD;
typedef pair<int, int> pii;
typedef pair<db, db> pdd;
typedef pair<ll, ll> pll;


int solve()
{
	int n;
	string s;
	if (!(cin >> n >> s))
		return 1;
	
	int ans = 0;
	vector<string> as;
	string curr = "";
	FOR (i, 0, n)
	{
		if (s[i] == 'a')
			curr += s[i];
		else
		{
			if (sz(curr) > 1)
				ans += sz(curr);
			curr = "";
		}
	}
	if (sz(curr) > 1)
		ans += sz(curr);
	cout << ans << '\n';
	
	
	return 0;
}

int32_t main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int TET = 1e9;
	//cin >> TET;
	for (int i = 1; i <= TET; i++)
	{
		if (solve())
		{
			break;
		}
		#ifdef ONPC
			cerr << "_____________________________\n";
		#endif
	}
	#ifdef ONPC
		cerr << "\nfinished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec\n";
	#endif
	return 0;
}