#include <bits/stdc++.h>
using namespace std;
vector<long long int> v[100005];
bool vis[100005];
map<pair<long long int, long long int>, long long int> cost;
long long int modular_pow(long long int base, long long int exponent) {
  long long int result = 1;
  while (exponent > 0) {
    if (exponent % 2 == 1) result = (result * base) % 1000000007;
    exponent = exponent >> 1;
    base = (base * base) % 1000000007;
  }
  return result % 1000000007;
}
bool mycmp(pair<long long int, long long int> a,
           pair<long long int, long long int> b) {
  if (a.second < b.second) return true;
  return false;
}
vector<int> prime;
bool isPrime[1000005];
void seive() {
  memset(isPrime, true, sizeof(isPrime));
  isPrime[2] = 1;
  for (int i = 2; i <= 1000000; i++) {
    if (isPrime[i]) {
      prime.push_back(i);
      for (int j = i * 2; j <= 1000000; j += i) isPrime[j] = 0;
    }
  }
}
long long int query(long long int *BIT, long long int index) {
  long long int sum = 0;
  for (; index > 0; index -= index & -index) sum += BIT[index];
  return sum;
}
void update(long long int *BIT, long long int maxval, long long int index,
            long long int val) {
  for (; index <= maxval; index += index & -index) BIT[index] += val;
}
long long int totalCost[1000005];
long long int maxcost = 0, maxnode = 1;
void dfs(long long int a, long long int costi) {
  if (vis[a]) return;
  vis[a] = 1;
  if (costi > maxcost) {
    maxcost = costi, maxnode = a;
  }
  long long int len = v[a].size();
  for (int i = 0; i < len; i++) {
    if (!vis[v[a][i]]) {
      dfs(v[a][i], costi + cost[{a, v[a][i]}]);
    }
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int i, j, k, l, m, n, a, b, h;
  string second;
  cin >> n;
  cin >> second;
  l = second.length();
  string dummy = "";
  for (i = 0; i < l; i++)
    if (second[i] == 'H')
      dummy = 'H' + dummy;
    else
      dummy = dummy + 'T';
  string nstr = dummy + dummy;
  long long int mini = LLONG_MAX, curr = 0;
  for (i = 0; i < l; i++) {
    curr = 0;
    for (j = 0, k = i; j < l; j++, k++)
      if (second[j] != nstr[k]) curr++;
    mini = min(mini, curr / 2);
  }
  cout << mini;
}
