#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < n;++i)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
const int inf = 0x3f3f3f3f;
const int Mod = 1e9 + 7;
inline int sign(int a){ return (a&1) ? (Mod-1) : 1; }
inline void uadd(int &a, int b){ a += b-Mod; a += (a>>31) & Mod; }
inline void usub(int &a, int b){ a -= b, a += (a>>31) & Mod; }
inline void umul(int &a, int b){ a = (int)(1ll * a * b % Mod); }
inline int add(int a, int b){ a += b-Mod; a += (a>>31) & Mod; return a; }
inline int sub(int a, int b){ a -= b, a += (a>>31) & Mod; return a; }
inline int mul(int a, int b){ a = (int)(1ll * a * b % Mod); return a; }
int qpow(int b, int p){ int ret = 1; while(p){ if(p&1) umul(ret, b); umul(b, b), p >>= 1; } return ret; }
void chmax(int &a, int b){ (b > a) ? (a = b) : 0; }

int n;
string s;
const string targ = "spbsu";
int nxt[26][100100], pre[26][100100];

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> n >> s;
	rep(i, 26) nxt[i][n] = n;
	for(int i = n-1; i >= 0; --i){
		rep(j, 26)
			nxt[j][i] = nxt[j][i+1];
		nxt[s[i] - 'a'][i] = i;
	}
	rep(i, 26) pre[0][i] = 0;
	rep(i, n){
		rep(j, 26) pre[j][i+1] = pre[j][i];
		pre[s[i] - 'a'][i+1] = i+1;
	}

	int ans = inf;
	rep(i, n) if(s[i] == targ[2]){
		deque<int> ps;
		ps.emplace_back(i);
		int p = i;
		for(int j = 3; j < 5; ++j){
			//cout << j << endl;
			p = nxt[targ[j] - 'a'][p + 1];
			ps.emplace_back(p);
			if(p >= n) break;
		}
		if(p >= n) continue;
		p = i;
		for(int j = 1; j >= 0; --j){
			//cout << j << endl;
			p = pre[targ[j] - 'a'][p] - 1;
			ps.emplace_front(p);
			if(p < 0) break;
		}
		if(p < 0) continue;
		//cout << (int)ps.size() << endl;
		//rep(j, 5) cout << ps[j] << " ";
		//cout << endl;
		ans = min(ans, (ps[2] - ps[1] - 1) + (ps[3] - ps[2] - 1) + (ps[2] - ps[0] - 2) + (ps[4] - ps[2] - 2));
	}
	cout << ans << "\n";

	return 0;
}