#include <bits/stdc++.h>
using namespace std;
const int maxn=2e6+10;
int len,n;
string s;
int id,mx;
char ch[maxn];
int r[maxn],ans;
int main() {
	scanf("%d",&len);
	cin>>s;
	ch[++n]='$',ch[++n]='#';
	for (int i=0;i<len;i++)
	  ch[++n]=s[i],ch[++n]='#';
	ch[++n]='@';
	for (int i=1;i<n;i++) {
		if (mx>i) r[i]=min(mx-i,r[2*id-i]);
		else r[i]=1;
		if (ch[id]=='#' && ch[i]=='#' && i-id<r[i] && mx>i) {
			ans=max(ans,((i-id)<<1));
		}
		while (ch[i+r[i]]==ch[i-r[i]]) r[i]++;
		if (i+r[i]>mx) {
			mx=i+r[i];
			id=i;
		}
	} 
	printf("%d\n",ans);
	return 0;
}