#include <bits/stdc++.h>
using namespace std;

int main() {
  string S;
  cin >> S;
  int N = S.size();
  vector<int> V(N);
  S.insert(S.size(), " ");
  for (int i = 0, cnt = 1; i < N; i++) {
    if (S.at(i) != S.at(i + 1)) V.at(i) = cnt, cnt = 1;
    else cnt++;
  }
  for (int i = N - 1; i >= 0; i--) {
    if (!V.at(i)) V.at(i) = V.at(i + 1);
  }
  int ans = 0;
  for (int i = 0; i + 1 < N; i++) {
    if (V.at(i) != V.at(i + 1)) ans = max(ans, min(V.at(i), V.at(i + 1)) * 2);
  }
  cout << ans << "\n";
}