#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
using ll = long long;
using graph = vector<vector<int>>;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
vector<int> dh = {-1,0,1,0,-1,1,1,-1};
vector<int> dw = {0,1,0,-1,1,1,-1,-1};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  string s; cin >> s;
  ll len = s.length();
  ll ans = 0;
  for(int i=0;i<len-2;i++) {
    set<char> set;
    set.insert(s.at(i));
    set.insert(s.at(i+1));
    set.insert(s.at(i+2));
    if (set.size()==2) ans++;
  }
  cout << ans << "\n";
  return 0;
}