#include<bits/stdc++.h>
using namespace std;
 
int main()
{
	int n, curr, ans;
	cin>>n;
	vector<int> arr(n);
	for (int i=0; i<n; i++)
	cin>>arr[i];
	vector<int> count;
	curr = 1;
	for (int i=1; i<n; i++)
	{
		if (arr[i] == arr[i-1])
		{
			curr += 1;
		}
		else
		{
			count.push_back(curr);
			curr = 1;
		}
	}
	count.push_back(curr);
	ans = 0;
	for (int i=1; i<count.size(); i++)
	{
		ans = max(ans, min(count[i-1], count[i]));
	}
	cout<<ans*2<<endl;
	return(0);
}

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OQoyIDIgMSAxIDEgMiAyIDIgMgo=

9
2 2 1 1 1 2 2 2 2