#include <bits/stdc++.h>
#define int long long
#define double long double
using namespace std;
typedef unsigned long long ull;
typedef long long ll;

const int N = 1e5 + 10;
int nx[N][2], pre[N][2];
void solve()
{
	int n;
	string s;
	cin >> n >> s;
	s = '\0' + s;
	for (int i = 0; i < 2; ++i)
		nx[n][i] = n + 1;
	for (int i = n - 1; i; --i)
	{
		for (int j = 0; j < 2; ++j)
			nx[i][j] = nx[i + 1][j];
		if (s[i + 1] == 's')
			nx[i][0] = i + 1;
		if (s[i + 1] == 'u')
			nx[i][1] = i + 1;
	}
	for (int i = 0; i < 2; ++i)
		pre[1][i] = 0;
	for (int i = 2; i <= n; ++i)
	{
		for (int j = 0; j < 2; ++j)
			pre[i][j] = pre[i - 1][j];
		if (s[i - 1] == 'p')
			pre[i][0] = i - 1;
		if (s[i - 1] == 's')
			pre[i][1] = i - 1;
	}
	int ans = 1e18;
	for (int i = 1; i <= n; ++i)
		if (s[i] == 'b')
		{
			int pos = i, d[4];
			for (int j = 0; j < 2; ++j)
			{
				if (nx[pos][j] == n + 1)
				{
					cout << ans;
					return;
				}
				d[j] = nx[pos][j] - pos, pos = nx[pos][j];
			}
			pos = i;
			bool flag = true;
			for (int j = 0; j < 2; ++j)
			{
				if (!pre[pos][j])
					flag = false;
				d[j + 2] = pos - pre[pos][j], pos = pre[pos][j];
			}
			if (flag)
				ans = min(ans, 2 * d[0] + 2 * d[2] + d[3] + d[1] - 6);
		}
	cout << ans;
}
signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);

	// int T;
	// cin >> T;
	// while (T--)
	// 	solve();
	solve();
	return 0;
}