#include <bits/stdc++.h>

using namespace std;

#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--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef double db;

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int n;
	cin >> n;
	string s;
	cin >> s;
	int ans = 0;
	FOR (i, 0, n)
	{
		int j = i + 1;
		while (j < n && s[j] == s[i])
			j++;
		if (s[i] == 'a' && j - i > 1)
			ans += j - i;
		i = j - 1;
	}
	cout << ans << '\n';
	
	return 0;
}