Just A String

  #include<bits/stdc++.h>     
  using namespace std; 
  typedef long long  ll;
  typedef pair<ll,ll> pll; 
  #define pb(x) push_back(x)     
  typedef unsigned long long  ull;     
  #define mem(A, X) memset(A, X, sizeof A)
  #define ford(i,l,u) for(ll (i)=(ll)(l);(i)>=(ll)(u);--(i))
  #define foreach(e,x) for(__typeof(x.begin()) e=x.begin();e!=x.end();++e)
  #define fori(i,l,u) for(ll (i)=(ll)(l);(i)<=(ll)(u);++(i))   
  typedef pair<int,int> pii;
  #define mp  make_pair
  #define sec second
  #define fir first 

  const ll mod=1e9+7;
  const ll Maxn=2e3+10;


   ll Next[Maxn];

   void GetNext(char *p,ll m)
   {
       Next[0]=Next[1]=0;

       fori(i,1,m-1)
       {
        ll j=Next[i];
        while(j&&p[i]!=p[j]) j=Next[j];
        Next[i+1]= p[i]==p[j] ? j+1:0;
       }
   }

   ll Common[Maxn];
   void Find(char *s,char *p,ll m)
   {
    GetNext(p,m);
    ll n=strlen(s);
    //fori (i,0,m-1) cout<<Next[i]<<" ";
    //cout<<endl;
    ll j=0;
    //fori (i,0,m-1) printf("%d ",Next[i]);
    //printf("\n j: ");
    fori (i,0,n-1) {
      while(j&&s[i]!=p[j]) j=Next[j]; 
      if(s[i]==p[j]) j++;

      //printf("__%d  i-j+1: %d ",j,i-j+1);
      if(j==0) Common[i]=0;
        else Common[i]=j;
      if(j==m) j=Next[j];// 排除越界访问。
    } 
    //puts("");
   }


  int main()
  {
       std::ios::sync_with_stdio(false);
       //freopen("in.txt","r",stdin);
       int T;
       while(scanf("%d",&T) != EOF)
       {
        char s[Maxn];
        scanf("%s",s); 
        ll n = strlen(s);
        ll ret=0;
        fori (j,1,n) {
          fori(di,0,n-1) Common[di]=0;
          Find(s, s + (n-j), j);   
          //printf("%s___\n",s + (n - j ));
         // fori (di, 0, n-1) printf("%d ",Common[di]);
         // puts("");
          //puts("");
          fori (id, 0, n-1) {
            ll A,B,C,i; 
            B = Common[id];
            i=id+1;
            A = i - B;
            C = j - B;
            ll temp = A * B * B * C;
            //cout<<"A B C:"<<A<<" "<<B<<" "<<C<<"  temp: "<<temp<<endl;
            //cout<<temp<<endl;
            ret= ret ^ temp;
          }
        }
        printf("%lld\n",ret);
       }   
    return 0;
  }