#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e6 + 11;
string s;
bool vis[maxn];
int n;
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> s;
  n = s.length();
  vector<pair<int, int> > vec, tmp;
  for (int i = 0; i < n; i++) {
    if (vec.empty() || s[vec.back().first] != s[i])
      vec.emplace_back(i, i);
    else {
      pair<int, int> p = vec.back();
      vec.pop_back();
      vec.emplace_back(p.first, i);
    }
  }
  int ans = 0;
  while (vec.size() > 1) {
    for (int i = 0; i < (int)(vec).size(); i++) {
      int sub = 2 - (i == 0 || i == (int)(vec).size() - 1);
      if (vec[i].second >= vec[i].first + sub) {
        if (tmp.empty() || s[tmp.back().first] != s[vec[i].first]) {
          vec[i].second -= sub;
          tmp.push_back(vec[i]);
        } else {
          pair<int, int> p = tmp.back();
          tmp.pop_back();
          p.second += vec[i].second - vec[i].first + 1 - sub;
          tmp.push_back(p);
        }
      }
    }
    ans++;
    tmp.swap(vec);
    tmp.clear();
  }
  cout << ans << endl;
  return 0;
}
