#include <iostream>
#include <vector>

using namespace std;
using LL = long long;
using ULL = unsigned long long;

constexpr int INF = 1 << 30;
constexpr LL INFL = 1L << 62;
//constexpr int MOD = 998244353;

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

    vector<int> AB{1};
    for (int i = 1; i < S.size(); i++) {
        if (S[i] != S[i - 1]) {
            AB.push_back(1);
        } else {
            AB.back()++;
        }
    }

    int ans = 0;
    for (int i = 0; i < AB.size() - 1; i++) {
        ans = max(ans, min(AB[i], AB[i + 1]) * 2);
    }

    cout << ans << endl;
}