#include<bits/stdc++.h>
using namespace std ;
typedef long long ll ;
typedef unsigned long long ull ;
typedef pair < int , int > pii ;
typedef vector < int > vi ;
#define fi first
#define se second
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()

const int MAXN = 1e5 + 7 ;

int n ;
string a ;

int nxt[ MAXN ][ 26 ] ;
int prv[ MAXN ][ 26 ] ;

void solve ( ) {
    cin >> n ;
    cin >> a ;
    string spec = "spbsu" ;
    for ( int i = 0 ; i < 26 ; ++ i ) {
        nxt[ n ][ i ] = n ;
    }
    for ( int i = n - 1 ; i >= 0 ; -- i ) {
        for ( int j = 0 ; j < 26 ; ++ j ) {
            nxt[ i ][ j ] = nxt[ i + 1 ][ j ] ;
        }
        nxt[ i ][ ( a[ i ] - 'a' ) ] = i ;
    }
    for ( int i = 0 ; i < 26 ; ++ i ) {
        prv[ 0 ][ i ] = -1 ;
    }
    prv[ 0 ][ ( a[ 0 ] - 'a' ) ] = 0 ;
    for ( int i = 1 ; i < n ; ++ i ) {
        for ( int j = 0 ; j < 26 ; ++ j ) {
            prv[ i ][ j ] = prv[ i - 1 ][ j ] ;
        }
        prv[ i ][ ( a[ i ] - 'a' ) ] = i ;
    }
    int ans = 10 * MAXN ; 
    for ( int i = 0 ; i < n ; ++ i ) {
        if ( a[ i ] != 'b' ) { continue ; }
        int lst1 = prv[ i ][ 'p' - 'a' ] ;
        int nxt1 = nxt[ i ][ 's' - 'a' ] ;
        if ( lst1 <= 0 || nxt1 >= n - 1 ) { continue ; }
        int lst2 = prv[ lst1 - 1 ][ 's' - 'a' ] ;
        int nxt2 = nxt[ nxt1 + 1 ][ 'u' - 'a' ] ;
        if ( lst2 < 0 || nxt2 >= n ) { continue ; }
        int cand = ( ( i - 1 ) - lst1 ) + ( ( i - 2 ) - lst2 ) ;
        cand += ( nxt1 - ( i + 1 ) ) + ( nxt2 - ( i + 2 ) ) ;
        ans = min ( ans , cand ) ;
    }
    cout << ans << "\n" ;
}

int main ( ) {
    ios_base :: sync_with_stdio ( false ) ;
    cin.tie ( NULL ) ;
    int t = 1 ; // cin >> t ;
    while ( t -- ) { solve ( ) ; }
    return 0 ;
}