In this HackerEarth Holiday Season problem solution, It's a holiday season for all school students around the world! Unfortunately, Mahamba is busy preparing for International Olympiad in Informatics, which will be held in Tehran, Iran. He is now facing a new challenge from his teacher Aceka, and it goes something like this:

You have a string x of length N, which consists of small English letters. You have to find the number of indexes a, b, c and d, such that 1 <= a < b < c < d <= N and xa == xc, as well as xb == xd.

He is baffled and definitely needs some help. So, you, the best programmer in Lalalandia, decided to give him a hand!

## HackerEarth Holiday Season problem solution.

`#include <map>#include <set>#include <list>#include <cmath>#include <ctime>#include <deque>#include <queue>#include <stack>#include <string>#include <bitset>#include <cstdio>#include <limits>#include <vector>#include <climits>#include <cstring>#include <cstdlib>#include <fstream>#include <numeric>#include <sstream>#include <cassert>#include <iomanip>#include <iostream>#include <algorithm>#include <unordered_set>#include <unordered_map>using namespace std;#define f first#define s second#define pb push_back#define pp pop_back#define mp make_pair#define ll long long#define ld double#define ull unsigned long long#define PI pair < int, int > const int N = 2050;const int M = 123;const ld Pi = acos(-1);const ll Inf = 1e18;const int inf = 1e9;const int mod = 1e9 + 7;const int Sz = 501;const int MOD = 1e9 + 7;void add(int &a, int b) {  a += b;  if (a >= mod) a -= mod;}int mult(int a, int b) {  return 1ll * a * b % mod;}int sum(int a, int b) {  add(a, b);  return a;}int n, cnt;char a[N];ll ans;void solve() {   cin >> n;  assert(1 <= n && n <= 2000);  for (int i = 1;i <= n;i++) {    cin >> a[i];    assert('a' <= a[i] && a[i] <= 'z');  }   for (int i = 1;i <= n;i++) {    ll now = 0;    for (int j = i + 1;j <= n;j++) {      if (a[j] == a[i]) {        ans += now;      }      now += cnt[a[j] - 'a'];    }    cnt[a[i] - 'a']++;  }  cout << ans << endl;}int main() {  #ifdef wws   freopen("in", "r", stdin);  #endif   ios_base::sync_with_stdio(0);  int tt = 1;   while(tt--) solve();  return 0;}`