ＴＬＥ　＃２　＃５　＃７求大佬调

ｒｔ

#include<bits/stdc++.h>
using namespace std;
char s[114514*5];
int n,ans=0;
int cnt=1,fail[114514*5],trans[114514],dep[114514*5],len[114514*5],ch[114514*5][26];
signed main(){
    cin >> n;
    cin >> s+1;
    s[0]='#';

    int las=0;
    fail[0]=1;
    len[1]=-1;
    for(int i=1;i<=n;i++){
        //if(i!=1) s[i]=(s[i]-97+ans)%26+97;
        while(s[i-len[las]-1]!=s[i]) las = fail[las];
        if(!ch[las][s[i]-'a']){
            len[++cnt]=len[las]+2;
            int j = fail[las];
            while(s[i-len[j]-1]!=s[i]) j = fail[j];
            fail[cnt]=ch[j][s[i]-'a'];
            ch[las][s[i]-'a']=cnt;
            if(len[cnt]<=2) trans[cnt] = fail[cnt];
            else {
                int tmp = trans[las];
                while(s[i-len[tmp]-1]!=s[i] or (len[tmp]+2)*2>len[cnt]) tmp = fail[tmp];
                trans[cnt] = ch[tmp][s[i]-'a'];
            }
            dep[cnt]=dep[fail[cnt]]+1;
        }
        las = ch[las][s[i]-'a'];
    }
    for(int i=1;i<=n;i++){
        if(len[trans[i]]*2==len[i] and len[trans[i]]%2==0) ans = max(ans,len[i]);
    }
    cout << ans;
    return 0;
}