1 #include<cstdio> 2  3 #include<cstdlib> 4  5 #include<cmath> 6  7 #include<cstring> 8  9 #include<algorithm>10 11 #include<iostream>12 13 #include<vector>14 15 #include<map>16 17 #include<set>18 19 #include<queue>20 21 #include<string>22 23 #define inf 100000000024 25 #define maxn 1000000+526 27 #define maxm 500+10028 29 #define eps 1e-1030 31 #define ll long long32 33 #define pa pair<int,int>34 35 #define for0(i,n) for(int i=0;i<=(n);i++)36 37 #define for1(i,n) for(int i=1;i<=(n);i++)38 39 #define for2(i,x,y) for(int i=(x);i<=(y);i++)40 41 #define for3(i,x,y) for(int i=(x);i>=(y);i--)42 43 #define mod 100000000744 45 using namespace std;46 47 inline int read()48 49 {50 51     int x=0,f=1;char ch=getchar();52 53     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}54 55     while(ch>=‘0‘&&ch<=‘9‘){x=10*x+ch-‘0‘;ch=getchar();}56 57     return x*f;58 59 }60 int n,p[maxn];61 char s[maxn],st[maxn];62 63 int main()64 65 {66 67     freopen("input.txt","r",stdin);68 69     freopen("output.txt","w",stdout);70 71     n=read();scanf("%s",st+1);72     for1(i,n)s[i<<1]=st[i];n<<=1;n++;73     for(int i=1;i<=n;i+=2)s[i]=‘#‘;74     int id=0,mx=0;75     for(int i=1;i<=n;i+=2)76     {77         if(mx>i)p[i]=min(p[2*id-i],mx-i);78         while(i-p[i]>0&&i+p[i]<=n&&s[i-p[i]]==s[i+p[i]])p[i]++;79         if(i+p[i]>mx)mx=i+p[i],id=i;80     }81     int ans=0;82     for(int i=1;i<=n;i+=2)83     {84         int j=(p[i]-1)>>1;85         if(j&1)j--;86         for(;j>0&&2*j>ans;j-=2)87          if(p[i-j]-1>=j&&p[i+j]-1>=j)ans=max(ans,2*j);88     }89     printf("%d\n",ans);90 91     return 0;92 93 }