#include <bits/stdc++.h>
using namespace std;
int main() {
  int count = 0;
  int res = 0;
  char cur = 'A';
  while (cur) {
    cin.get(cur);
    if (cur == 'S')
      count++;
    else if (cur == 'T')
      count--;
    if (count < 0) {
      res++;
      count = 0;
    }
  }
  cout << 2 * res << endl;
}
