import re
input()
l = [*map(len, re.findall(r'1+|2+', input()[::2]))]
print(max(map(min, zip(l, l[1:]))) * 2)
#include<iostream>
#include<algorithm>
using namespace std;
const int maxi=1e5+9;
int t[maxi]={0};
int window_search(int len)
{
int maxx=0;
int i=1,j=2;
int num1=0,num2=0;
int num=0;
while(j<=len)
{
num1=1, num2=0;
while(t[j]==t[j-1]){
j++;
num1++;
if(j>len) return maxx;
}
//j++;
while(t[j]!=t[i]){
j++;
num2++;
if(j>len){
num=min(num1,num2);
num*=2;
maxx=max(maxx,num);
return maxx;
}
}
j--;
num=min(num1,num2);
num*=2;
maxx=max(maxx,num);
i=i+num1;
j=i+1;
}
return maxx;
}
int main()
{
int n;
scanf("%d",&n);
for(int i=1;i<=n;i++){
scanf("%d",&t[i]);
}
int ans=window_search(n);
printf("%d",ans);
return 0;
}
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