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

int main() {
  string s;
  cin>>s;
  int n = s.length();
  int dp[n];
  dp[0] = 0;
  for (int i=1; i<n; i++) {
    if (i-dp[i-1]-1 >= 0 && s[i-dp[i-1]-1] != s[i]) {
      dp[i] = dp[i-1] + 2;
    } else {
      if (s[i] != s[i-1]) {
        dp[i] = 2;
      } else {
        dp[i] = 0;
      }
    }
  }
  int ans = 0;
  for (int i=0; i<n; i++) {
    ans = max(dp[i], ans);
  }
  cout<<ans<<endl;
}