#include <bits/stdc++.h>
using namespace std;
const long long N = 1e5 + 5;
const long long mod = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  string str;
  cin >> str;
  long long n = str.length();
  vector<pair<long long, long long> > arr;
  arr.push_back(make_pair(1, str[0] - 'a'));
  for (long long i = 1; i < n; i++) {
    if (str[i] == str[i - 1])
      arr[arr.size() - 1].first++;
    else
      arr.push_back(make_pair(1, str[i] - 'a'));
  }
  long long ans = 0;
  while (arr.size() > 1) {
    ans++;
    vector<pair<long long, long long> > tmp;
    for (long long i = 0; i < arr.size(); i++) {
      if (i == 0 || i == arr.size() - 1)
        arr[i].first -= 1;
      else
        arr[i].first -= 2;
      if (tmp.size() == 0 || arr[i].second != tmp[tmp.size() - 1].second) {
        if (arr[i].first > 0) tmp.push_back(arr[i]);
      } else if (arr[i].first > 0)
        tmp[tmp.size() - 1].first += arr[i].first;
    }
    arr = tmp;
  }
  cout << ans;
}
