#include <bits/stdc++.h>
using namespace std;

typedef long long ll; typedef unsigned long long ull;
const int inf = 1e9; const ll llnf = 4e18;

template< class Tp > void chkmax( Tp &x , Tp y ) { x = max( x , y ); }
template< class Tp > void chkmin( Tp &x , Tp y ) { x = min( x , y ); }

void solve( ) {
	int n; string a; cin >> n >> a; string b = "spbsu";

	vector< vector< int > > suf( n , vector< int >( 26 , n ) );
	for( int i = n - 1; i >= 0; i -- ) { if( i < n - 1 ) suf[i] = suf[i + 1]; suf[i][a[i] - 'a'] = i; }
	vector< vector< int > > pre( n , vector< int >( 26 , -1 ) );
	for( int i = 0; i <= n - 1; i ++ ) { if( i > 0 ) pre[i] = pre[i - 1]; pre[i][a[i] - 'a'] = i; }

	int ans = inf;
	for( int i = 0; i < n; i ++ ) if( a[i] == b[2] ) {
		vector< int > p( 5 );
		p[2] = i;
		p[1] = pre[p[2]][b[1] - 'a']; if( p[1] == -1 ) continue;
		p[0] = pre[p[1]][b[0] - 'a']; if( p[0] == -1 ) continue;
		p[3] = suf[p[2]][b[3] - 'a']; if( p[3] == n ) continue;
		p[4] = suf[p[3]][b[4] - 'a']; if( p[4] == n ) continue;

		chkmin( ans , p[4] - p[0] + p[3] - p[1] - 6 );
	}
	cout << ans << "\n";
}

int main( ) {
	ios::sync_with_stdio( 0 ), cin.tie( 0 ), cout.tie( 0 );
	int T = 1; while( T -- ) solve( ); return 0;
}