// This Code was made by Chinese_zjc_.
#include <bits/stdc++.h>
// #define debug
int n;
std::string s;
int dp[100005][6], ans = INT_MAX;
void cmin(int &A, int B) { A = std::min(A, B); }
signed main()
{
    std::ios::sync_with_stdio(false);
    std::cin >> n >> s;
    std::memset(dp, 0x3f, sizeof(dp));
    for (int i = 0; i != n; ++i)
    {
        dp[i][0] = 0;
        if (s[i] == 's')
            cmin(dp[i + 1][1], dp[i][0]);
        if (s[i] == 'p')
            cmin(dp[i + 1][2], dp[i][1]);
        if (s[i] == 'b')
            cmin(dp[i + 1][3], dp[i][2]);
        if (s[i] == 's')
            cmin(dp[i + 1][4], dp[i][3]);
        if (s[i] == 'u')
            cmin(dp[i + 1][5], dp[i][4]);
        for (int j = 0; j <= 5; ++j)
            cmin(dp[i + 1][j], dp[i][j] + (j <= 2 ? j : 5 - j));
        ans = std::min(ans, dp[i][5]);
    }
    ans = std::min(ans, dp[n][5]);
    std::cout << ans << std::endl;
    return 0;
}