#include<iostream>

 #include<cstdio>

 #include<cstring>

 #define M 1000010

 using namespace std;

 int n,ans,l;

 int len[M];

 char s[M],a[M];

 void change()

 {

     s[]=s[]='#';

     for(int i=;i<n;i++)

     {

         s[i*+]=a[i];

         s[i*+]='#';

     }

     n=n*+;

     s[n]=;

 }

 void manacher()

 {

     int mx=,mid;

     for(int i=;i<n;i++)

     {

         if(i<mx) len[i]=min(len[mid*-i],mx-i);

         else len[i]=;

         while(s[i-len[i]]==s[i+len[i]]) len[i]++;

         if(i+len[i]>mx)

         {

             mx=i+len[i];

             mid=i;

         }

     }

 }

 int main()

 {

     scanf("%d",&n);

     scanf("%s",a);

     change();

     manacher();

     for(int i=;i<=n;i+=)

     {

         l=(i-len[i]+i+)/;

         if(l%==) l++;

         while(l<=i&&l+len[l]<i) l+=;

         ans=max(ans,((i-l)/)*);

     }

     printf("%d",ans);

     return ;

 }