#include <bits/stdc++.h>
using namespace std;
int main() {
    int n;
    string s;
    cin >> n >> s;
    bool flag1 = true;
    bool flag2 = true;
    for(int i = 0; i < n; i++){
        if(s[i] == 'H')
            flag1 = false;
        else
            flag2 = false;
    }
    if(flag1 || flag2){
        cout << 0;
        return 0;
    }
    s += s;
    int maxx = 1000000000;
    for(int i = 0; i < n; i++){
        if(s[i] != 'T')
            continue;
        int cnt = 0; // final pattern : TTHHTT
        int l = i;   // s[l] must -> H
        int r = i+n-1; // s[r] must -> T
        while(s[r] == 'T' && r > i)
            r--;
        while(s[r] == 'H' && r > i)
            r--;
        while(s[l] == 'T' && l < i+n-1)
            l++;

        while(l < r){
            l++;
            r--;
            cnt++;
            while(s[l] == 'T' && l < i+n-1)
                l++;
            while(s[r] == 'H' && r > i)
                r--;

        }
        maxx = min(maxx, cnt);

    }
    cout << maxx ;
    return 0;
}