//#pragma GCC optimize("Ofast", "unroll-loops")
//#pragma GCC target("sse", "sse2", "sse3", "ssse3", "sse4")
#ifdef LOCAL
#include <iostream>
#include <cmath>
#include <algorithm>
#include <stdio.h>
#include <cstdint>
#include <cstring>
#include <string>
#include <cstdlib>
#include <vector>
#include <bitset>
#include <map>
#include <queue>
#include <ctime>
#include <stack>
#include <set>
#include <list>
#include <random>
#include <deque>
#include <functional>
#include <iomanip>
#include <sstream>
#include <fstream>
#include <complex>
#include <numeric>
#include <cassert>
#include <array>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <thread>
#else
#include <bits/stdc++.h>
#endif

#define all(a) a.begin(),a.end()
#define len(a) (int)(a.size())
#define mp make_pair
#define pb push_back
#define fir first
#define sec second
#define fi first
#define se second

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
typedef long double ld;

template<typename T>
inline bool umin(T &a, T b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<typename T>
inline bool umax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

#ifdef LOCAL
#define D for (bool _FLAG = true; _FLAG; _FLAG = false)
#define LOG(...) print(#__VA_ARGS__" ::", __VA_ARGS__) << endl
template <class ...Ts> auto &print(Ts ...ts) { return ((cerr << ts << " "), ...); }
#else
#define D while (false)
#define LOG(...)
#endif // LOCAL

const int max_n = -1, inf = 1000111222;



int main() {
//    freopen("input.txt", "r", stdin);
//    freopen("output.txt", "w", stdout);

    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    string s;
    cin >> s;
    int n = len(s);
    map <pii, ll> ans;
    map <int, ll> one, l, h;
    for (int i = 0; i < n; i++) {
        int cur = s[i] - 'a';
        for (auto &j : h) {
            int a = j.first;
            one[a] += j.second;
            int b = cur;
            if (a > b) {
                swap(a, b);
            }
            ans[{a, b}] -= j.second;
        }
        h[cur] += 1;
        l[cur] -= 1;
        l[16] += 1;
    }
    ll res = 0;
    int val[16] = {};
    for (int mask = 0; mask < (1 << 16); mask++) {
        for (int i = 0; i < 16; i++) {
            val[i] = bool(mask & (1 << i));
        }
        ll cur = 0;
        for (auto &j : ans) {
            cur += j.second * val[j.first.first] * val[j.first.second];
        }
        for (auto &j : one) {
            cur += j.second * val[j.first];
        }
        umax(res, cur);
    }
    cout << res << '\n';
}