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#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using PII = pair<int, int>;
template <typename T> using V = vector<T>;
template <typename T> using VV = vector<V<T>>;
template <typename T> using VVV = vector<VV<T>>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll INF = (1LL<<60);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a<=x&&x<b; }
template<typename T> T ceil(T a, T b) { return a/b + !!(a%b); }
template<class S,class T>
ostream &operator <<(ostream& out,const pair<S,T>& a){
  out<<'('<<a.first<<','<<a.second<<')';
  return out;
}
template<class T>
ostream &operator <<(ostream& out,const vector<T>& a){
  out<<'[';
  REP(i, a.size()) {out<<a[i];if(i!=a.size()-1)out<<',';}
  out<<']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

signed main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);

  string s;
  cin >> s;
  int n = s.size();

  int ret = 0;
  string t(s);
  REP(i, n) {
    // 回文が存在するか判定
    bool change = false;
    if(i>=1 && t[i] == t[i-1]) change = true;
    if(i>=2 && t[i] == t[i-2]) change = true;

    if(change) {
      set<char> st;
      if(i>=1) st.insert(t[i-1]);
      if(i>=2) st.insert(t[i-2]);
      st.insert(s[i]);
      if(i+1 < n) st.insert(s[i+1]);
      if(i+2 < n) st.insert(s[i+2]);
      char c = 'a';
      while(st.find(c) != st.end()) {
        c++;
      }
      t[i] = c;
      ret++;
    } else {
      t[i] = s[i];
    }
  }

  cout << ret << endl;

  return 0;
}