#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;


int main(){
  string s;
  cin >> s;

  vector<pair<int,int>> v;
  char prev = '.';
  int cnt = 0;
  rep(i,s.size()){
    if(s[i] != prev){
      if(prev != '.') v.push_back(make_pair(prev,cnt));
      prev = s[i];
      cnt = 1;
    }else{
      cnt++;
    }
  }
  v.push_back(make_pair(prev,cnt));

  int ret = 0;
  rep(i,v.size()-1){
    ret = max(ret, min(v[i].second, v[i+1].second));
  }
  REP(i,1,v.size()-1){
    if(v[i].second <= v[i-1].second + v[i+1].second){
      ret = max(ret, v[i].second);
    }
  }
  
  cout << ret*2 << endl;
  
  return 0;
}