#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int n = (int)s.size();
  string t = "";
  for (int i = 0; i < n / 2; ++i) t += "T";
  for (int i = 0; i < n / 2; ++i) t += "S";
  int cnt = 0;
  for (int i = 0; i < n; ++i) {
    if (s[i] != t[i]) cnt++;
  }
  cout << n - cnt << endl;
  return 0;
}
