#include<bits/stdc++.h>
using std::cin;
using std::cout;
const int N = 200005;
char s[N];
int nxt[N][26];
int pre[N][26];
int main() {
	int n;
	cin >> n;
	for(int i = 1;i <= n;++i) {
		cin >> s[i];
	}
	for(int i = n - 1;i >= 0;--i) {
		memcpy(nxt[i], nxt[i + 1], 26 << 2);
		nxt[i][s[i + 1] - 'a'] = i + 1;
	}
	for(int i = 2;i <= n;++i) {
		memcpy(pre[i], pre[i - 1], 26 << 2);
		pre[i][s[i - 1] - 'a'] = i - 1;
	}
	int ans = 1e9;
	for(int i = 1;i <= n;++i) {
		if(s[i] == 'b') {
			std::vector<int> o(5);
			o[2] = i;
			o[3] = nxt[o[2]]['s' - 'a'];
			o[4] = nxt[o[3]]['u' - 'a'];

			o[1] = pre[o[2]]['p' - 'a'];
			o[0] = pre[o[1]]['s' - 'a'];
			if(o[0] && o[4]) {
				int sum = 0;
				for(int i = 0;i < 5;++i) {
					sum += std::abs(o[2] + (i - 2) - o[i]);
				}
				ans = std::min(ans, sum);
			}
		}
	}
	cout << ans << '\n';
}