import sys, os, io
input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline
s = list(input().rstrip())
u, v = [], []
c, l = 0, s[0]
for i in s:
if l ^ i:
u.append(c)
v.append(l)
c, l = 0, i
c += 1
u.append(c)
v.append(l)
ans = 0
while len(u) > 1:
ans += 1
u[0] += 1
u[-1] += 1
u0, v0 = [], []
for i, j in zip(u, v):
c = i - 2
if c <= 0:
continue
if not v0 or v0[-1] ^ j:
u0.append(c)
v0.append(j)
else:
u0[-1] += c
u, v = u0, v0
print(ans)#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define For(i,a,b) for(int i=a;i<b;i++)
#define Forn(i,a,b) for(int i=a;i>=0;i--)
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define eb emplace_back
#define LL long long
#define first(x) get<0>(x)
#define second(x) get<1>(x)
#define third(x) get<2>(x)
using namespace std;
void solve(){
string s;
cin>>s;
int n=s.length();
vector<pair<int,int>> vec;
int cnt=1;
for(int i=1;i<n;i++){
if(s[i]==s[i-1]){
cnt++;
}
else{
vec.pb({s[i-1]-'a',cnt});
cnt=1;
}
}
vec.pb({s[n-1]-'a',cnt});
vector<pair<int,int>> new_vec;
int ans=0;
while(true){
int sz=vec.size();
/*
for(auto p:vec){
cout<<p.first<<" "<<p.second<<endl;
}
cout<<endl;
*/
if(sz<=1) break;
ans++;
for(int i=0;i<sz;i++){
if(i==0 || i==sz-1){
vec[i].second--;
}
else vec[i].second-=2;
}
/*
cout<<"here2"<<endl;
for(auto p:vec){
cout<<p.first<<" "<<p.second<<endl;
}
cout<<endl;
*/
int i=0, j=1, cnt=0;
while(i<sz){
if(vec[i].second>0){
cnt=vec[i].second;
break;
}
i++;
}
//cout<<"i="<<i<<endl;
if(i==sz){
break;
}
j=i+1;
while(j<sz){
if(vec[j].second>0){
if(vec[j].first==vec[i].first){
cnt+=vec[j].second;
}
else{
new_vec.pb({vec[i].first,cnt});
i=j;
cnt=vec[j].second;
}
}
j++;
}
new_vec.pb({vec[i].first,cnt});
vec=new_vec;
new_vec.clear();
}
cout<<ans<<endl;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
solve();
return 0;
}1373A - Donut Shops | 26A - Almost Prime |
1656E - Equal Tree Sums | 1656B - Subtract Operation |
1656A - Good Pairs | 1367A - Short Substrings |
87A - Trains | 664A - Complicated GCD |
1635D - Infinite Set | 1462A - Favorite Sequence |
1445B - Elimination | 1656C - Make Equal With Mod |
567A - Lineland Mail | 1553A - Digits Sum |
1359B - New Theatre Square | 766A - Mahmoud and Longest Uncommon Subsequence |
701B - Cells Not Under Attack | 702A - Maximum Increase |
1656D - K-good | 1426A - Floor Number |
876A - Trip For Meal | 1326B - Maximums |
1635C - Differential Sorting | 961A - Tetris |
1635B - Avoid Local Maximums | 20A - BerOS file system |
1637A - Sorting Parts | 509A - Maximum in Table |
1647C - Madoka and Childish Pranks | 689B - Mike and Shortcuts |