#include<bits/stdc++.h>
using namespace std;
int d1[514514],d2[514514];
string s;
int n;
int main(){
	cin>>n;
	cin>>s;
	for(int i=0,l=0,r=-1;i<n;i++){
		int k;
		if(i>r){
			k=0;
		}
		else{
			k=min(d2[l+r-i+1],r-i+1);
		}
		while(i-k-1>=0&&i+k<n&&i+k<n&&s[i-k-1]==s[i+k]){
			k++;
		}
		d2[i]=k;
		k--;
		if(i+k>r){
			l=i-k-1;
			r=i+k;
		}
	}int cnt=0;
	int ans=0;
	for(int i=0;i<n;i++){
		if(d2[i]!=0&&d2[i]%2==0){
			if(i-d2[i]/2>=0)
			if(d2[i-d2[i]/2]==d2[i]/2){
				ans=max(ans,d2[i]*2);
			}
		}
	}
	cout<<ans;
	return 0;
}