#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;

int n, nxt[500005][26], prv[500005][26];
char ch[100005];

char pat[6] = "spbsu";
int pos[5];
int solve(int mid) {
    int ret = 0, p = mid;
    p = prv[p - 1]['p' - 'a'];
    if(p == 0) return INF;
    ret -= p - 1;
    p = prv[p - 1]['s' - 'a'];
    if(p == 0) return INF;
    ret -= p;
    p = nxt[mid + 1]['s' - 'a'];
    if(p == n + 1) return INF;
    ret += p - 3;
    p = nxt[p + 1]['u' - 'a'];
    if(p == n + 1) return INF;
    ret += p - 4;
    return ret;
}

int main() {
    scanf("%d%s", &n, ch + 1);
    for(int i = 0; i < 26; i++)
        nxt[n + 1][i] = n + 1;
    for(int i = n; i >= 1; i--) {
        for(int j = 0; j < 26; j++)
            nxt[i][j] = nxt[i + 1][j];
        nxt[i][ch[i] - 'a'] = i;
    }
    for(int i = 0; i < 26; i++)
        prv[0][i] = 0;
    for(int i = 1; i <= n; i++) {
        for(int j = 0; j < 26; j++)
            prv[i][j] = prv[i - 1][j];
        prv[i][ch[i] - 'a'] = i;
    }
    int ans = INF;
    for(int i = 1; i <= n; i++)
        if(ch[i] == 'b')
            ans = min(ans, solve(i));
    printf("%d\n", ans);
    return 0;
}