#include<bits/stdc++.h>
#include<cctype>
using namespace std;
int n;
const int N=1e6+10;
int a[N];
int ans;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	
	for(int i=1;i<=n/2;i++){
		int t=n/2;
		//cout<<i<<" "<<i+t<<" "<<a[i]<<" "<<a[i+3]<<endl;
		
		int j;
		if(i+t>n){
			j=i+t-n;
		}else if(i+t==n){
			j=1;
		}else{
			j=i+t;
		} 
		if(a[i]==a[j]){
			ans+=2;
		}
	}
	
	cout<<ans;
	return 0;
}

WA了，求调（悲）