#include<bits/stdc++.h>
using namespace std;
const int maxn=1e6+10;
char s[maxn<<1];
int f[maxn<<1];
int main()
{
	int n;
	scanf("%d",&n);
	s[0]='~';
    getchar();getchar();
	for(int i=1;i<=n;i++){
		scanf("%c",&s[2*i]);
		s[2*i-1]='|';
	}
	s[n=n*2+1]='|';
    //printf("%s\n",s);
	int mid=0,r=0,ans=0;
	for(int i=1;i<=n;i+=2){
		if(i<r)f[i]=min(f[mid*2-i],r-i);
        //printf("%d %d %d %d ",i,f[i],mid,r);
		if(i-f[i]<=mid)ans=max(ans,(i-mid)*2);
		while(s[i-f[i]-1]==s[i+f[i]+1])f[i]++;
		if(i+f[i]>r)mid=i,r=i+f[i];
        //printf("%d\n",f[i]);
	}
	printf("%d\n",ans);
	return 0;
}