#include<bits/stdc++.h>
using namespace std; 
 
#define fwd(i, a, n) for (int i = (a); i < (n); ++ i)
#define rep(i, n) fwd(i, 0, n)
#define all(X) begin(X), end(X)
#define sz(X) ((int)X.size())
#define st first
#define nd second
#define pii pair<int, int>
#define vi vector<int>
 
#ifdef LOC
template<typename Stream, typename T1, typename T2>
Stream& operator << (Stream& out, pair<T1, T2> a) {return out << "(" << a.st << ", " << a.nd << ")";}
 
template<typename Stream, typename T>
Stream &operator << (Stream& out, T v) {
	out << "{";
	int i = 0;
	for (auto x : v)
		out << x << ((++ i) != sz(v) ? ", " : "");
	return out << "}";
}
 
template<typename... Args>
void dump(Args... x) {((cerr << x << ", "), ...) << '\n';}
 
#define debug(x...) cerr << "[" #x "]: ", dump(x)
#else
#define debug(...) 0
#endif
 
using ll = long long;
 
 
int32_t main() {
	ios_base::sync_with_stdio(0), cin.tie(0);
	int n; cin>>n;
	string str; cin>>str;
	vector<array<int, 3>> l(n, {-1, -1, -1});
	vector<array<int, 3>> r(n, {-1, -1, -1});
	for(int i = 0; i < n; i++){
		if(i != 0)l[i] = l[i-1];
		if(str[i] == 's'){
			l[i][0] = i;
		}
		if(str[i] == 'p'){
			l[i][1] = i;
		}
		if(str[i] == 'u'){
			l[i][2] = i;
		}
	}
	for(int i = n-1; i >= 0; i--){
		if(i != n-1)r[i] = r[i+1];
		if(str[i] == 's'){
			r[i][0] = i;
		}
		if(str[i] == 'p'){
			r[i][1] = i;
		}
		if(str[i] == 'u'){
			r[i][2] = i;
		}
	}
	int res = 1e9;
	int a, b, c, d, e;
	for(int i = 0; i < n; i++){
		if(str[i] == 'b'){
			c = i;
			b = l[c][1];
			d = r[c][0];
			if(c != -1 && d != -1){
				a = l[b][0];
				e = r[d][2];
				if(a != -1 && e != -1){
					res = min(res, (c -b - 1) + (c -a - 2) + (d - c - 1) + (e - c - 2));
				}
			}
		}
	}
	cout<<res<<"\n";
	return 0;
}