#include <bits/stdc++.h>
#define FOR(i, a, b) for(int i = a; i <= b; ++i)
using namespace std;
#define Tp array<int,5>
const int _ = 2e6+6;

int a[_];
int be[_][5],en[_][5];
signed main() {
    #ifdef ONLINE_JUDGE
        ios::sync_with_stdio(false);
    #else
        freopen("a.in","r",stdin);
    #endif

    int n;
    string s;
    cin>>n>>s;
    s=' '+s;
    for(int i=1;i<=n;++i) {
        if(s[i]=='s') a[i]=1;
        if(s[i]=='p') a[i]=2;
        if(s[i]=='b') a[i]=3;
        if(s[i]=='u') a[i]=4;        
    }
    // 12314
    FOR(j,1,4) be[0][j]=-1e8;
    for(int i=1;i<=n;++i) {
        FOR(j,1,4) be[i][j]=be[i-1][j];
        be[i][a[i]]=i;
    }
    FOR(j,1,4) en[n+1][j]=1e8;
    for(int i=n;i>=1;--i) {
        FOR(j,1,4) en[i][j]=en[i+1][j];
        en[i][a[i]]=i;
    }
    int ans=0x3f3f3f3f;
    Tp tmp={1,2,3,1,4};
    for(int i=1;i<=n;++i) {
        if(a[i]==tmp[2]) {
            int b=be[i][tmp[1]];
            int c=i;
            int d=en[i][tmp[3]];
            if(abs(b)==1e8) continue;
            if(abs(d)==1e8) continue;

            int a=be[b][tmp[0]];
            int e=en[d][tmp[4]];
            if(abs(a)==1e8) continue;
            if(abs(e)==1e8) continue;

            int tot=0;
            tot+=(c-b-1)*2;
            tot+=b-a-1;
            tot+=(d-c-1)*2;
            tot+=e-d-1;
            ans=min(ans,tot);
        }
    }
    cout<<ans<<"\n";
    return 0;
}