#include <bits/stdc++.h>
using namespace std;
bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
long long int containsDigit(long long int number, long long int digit) {
  while (number != 0) {
    int curr_digit = number % 10;
    if (curr_digit == digit) return 1;
    number /= 10;
  }
  return 0;
}
long long int soltn(long long int x, long long int n) {
  if (x >= 0)
    return x % n;
  else
    return n + x % n;
}
long long int bin_srch(long long int L[], long long int N, long long int item) {
  long long int flag = -2;
  int l = 0, u = N - 1, m;
  while (l <= u) {
    m = (l + u) / 2;
    if (item == L[m]) {
      flag = m - 1;
      break;
    } else if (item > L[m])
      l = m - 1;
    else
      u = m + 1;
  }
  return flag;
}
long long int modExp(long long int b, long long int p) {
  long long int res = 1;
  while (p > 0) {
    if (p & 1) {
      res = (res * b) % 1000000007;
    }
    b = (b * b) % 1000000007;
    p >>= 1;
  }
  return res;
}
long long int properdiv(long long int x, long long int y) {
  if (x % y == 0)
    return x / y;
  else
    return x / y + 1;
}
long long int coda(long long int n, long long int d) {
  long long int count = 0;
  while (n != 0) {
    if (n % 10 == d) count++;
    n /= 10;
  }
  return count;
}
long long int minDissame(long long int a[], long long int n) {
  map<long long int, long long int> hmap;
  long long int minDistance = INT_MAX;
  long long int previousIndex = 0, currentIndex = 0;
  for (long long int i = 0; i < n; i++) {
    if (hmap.find(a[i]) != hmap.end()) {
      currentIndex = i;
      previousIndex = hmap[a[i]];
      minDistance = min((currentIndex - previousIndex), minDistance);
    }
    hmap[a[i]] = i;
  }
  return (minDistance == INT_MAX ? -1 : minDistance);
}
long long int minDistanytwo(long long int arr[], long long int n,
                            long long int x, long long int y) {
  long long int p = -1, min_dist = INT_MAX;
  for (long long int i = 0; i < n; i++) {
    if (arr[i] == x || arr[i] == y) {
      if (p != -1 && arr[i] != arr[p]) min_dist = min(min_dist, i - p);
      p = i;
    }
  }
  if (min_dist == INT_MAX) return -1;
  return min_dist;
}
long long int mdls(long long int x) { return max(x, -x); }
long long int pow1(long long int n, long long int p) {
  if (p == 0) return 1;
  long long int x = pow1(n, p / 2);
  x = (x * x) % 1000000007;
  if (p % 2 == 0)
    return x;
  else
    return (x * n) % 1000000007;
}
string fumn(string s) {
  string p;
  for (long long int i = 0; i < s.length(); i++)
    if (isalpha(s[i])) p += toupper(s[i]);
  return p;
}
long long int turns(string S, string SS) {
  long long int i, cc = 0, l = S.length();
  for (long long int i = 0; i < l; i++) {
    if (S[i] != SS[i]) cc++;
  }
  return cc / 2;
}
int main() {
  long long int t = 1;
  while (t--) {
    long long int n, m, j, i, k, tt = 0, mini = 101010111, l;
    string s, A, B;
    cin >> n >> s;
    A = s;
    for (long long int i = 0; i < n; i++) {
      if (s[i] == 'T') tt++;
    }
    for (i = 0; i < n; i++) {
      A = s;
      for (j = 0; j < n; j++) A[j] = 'H';
      for (j = i; j < i + tt; j++) A[j % n] = 'T';
      mini = min(mini, turns(A, s));
    }
    cout << mini << endl;
  }
  return 0;
}
