różnica xd :p

#include <bits/stdc++.h> // Tomasz Nowak
using namespace std;

#define FOR(i,a,n) for (auto i = (a), i##__ = (n); i <= i##__; ++i)
#define REP(i,n) FOR(i,0,(n)-1)
#define FORD(i,a,n) for (auto i = (a), i##__ = (n); i >= i##__; --i)
#define REPD(i,n) FORD(i,(n)-1,0)
#define ALL(x) x.begin(), x.end()
#define EB emplace_back
#define ST first
#define ND second
#define SZ(x) ((int)x.size())
#define RS resize
#define V vector
constexpr char nl = '\n';
template<class T, class B> void mini(T &&a, B &&b) { if (b < a) a = b; }
template<class T, class B> void maxi(T &&a, B &&b) { if (b > a) a = b; }
int pow2(int x) { return x < 2 ? 0 : sizeof(x) * 8 - __builtin_clz(x - 1); }

#define _S(zn, a...) typename enable_if<is_same<a, typename remove_reference<T>::type>::value zn 1, int>::type()
#define _F(func, a...) template<class T> auto func(T &&x) -> decltype(a)
template<class T> struct Off { T __a, __b; };
_F(O, _S(!=, string), Off<decltype(x.begin())>()) { return { ALL(x) }; }
_F(O, cerr << x, x) { return x; }
_F(O, x.first, x) { return x; }
#define _OP(a...) _F(operator<<, a, *this)
#define RTH return *this
struct Debug {
    ~Debug() { cerr << nl; }
    Debug& operator()(int x = 0) { REP(a, x+1) cout << "  "; RTH; }
    _OP(cerr << x) { cerr << O(x); RTH; }
    _OP(x.begin(), _S(!=, string)) {
        cerr <<  "{\n";
        for (auto a = x.begin(); a != x.end(); ++a)
    *this << "  " << distance(x.begin(), a) << ": " << O(*a) << '\n';
        RTH << "}";
    }
    _OP(x.first) { RTH << "(" << O(x.first) << ", " << O(x.second) << ")"; }
    _OP(x.__a) {
        cerr << "{";
        for (auto a = x.__a, b = x.__b; a != b; ++a)
    *this << O(*a) << (next(a) == b ? "" : ", ");
        RTH << "}";
    }
};
struct DebugOff {
    template<class T> DebugOff& operator<<(T&&) { RTH; }
    DebugOff& operator()(int = 0) { RTH; }
};
#ifdef DEBUG
# define D Debug()
# define DD(a...) a
#else
# define D DebugOff()
# define DD(...)
#endif
#define I(a...) #a ": " << a << "   "
#define TD(C, a...) _F(O, _S(==, C), x) { return x; } Debug& operator<<(Debug &d, C &x) { a; return d; }

using VI    = V<int>;
using VVI   = V<VI>;
using LL    = long long;
using VLL   = V<LL>;
using PII   = pair<int, int>;
using VPII  = V<PII>;
using VVPII = V<VPII>;
using VB    = V<bool>;

// end of templates v7

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    //WCZYTYWANIE DANYCH
    int n;
    cin >> n;
    VI word(n);
    REP(i, n)
    {
        char a;
        cin >> a;
        word[i] = a - 'a';
    }
    D << I(n) << I(word);
    //robienie rzeczy
    VVI pary;
    VI l_wyst(26);
    REP(i, n)
        ++l_wyst[word[i]];
    REP(i, 26)
        if(l_wyst[i])
            REP(j, 26)
                if(j != i && l_wyst[j] != 0)
                {
                    pary.EB(VI (0));
                    REP(k, n)
                        if(word[k] == i || word[k] == j)
                            pary[pary.size() - 1].EB(word[k]);
                }
    D << I(pary);
    int answ = 0;
    if(pary.empty())
    {
        cout << 0;
        return 0;
    }
    else
    {
        REP(i, SZ(pary))
        {
            int www = 0;
            int p = pary[i][0];
            REP(j, n)
            {
                if(pary[i][j] == p)
                    pary[i][j] = 1;
                else
                    pary[i][j] = -1;
            }
            int wynik = 0, suma = 0, suma_pop = 0, mini = 1e9;
            REP(j, n)
            {
                suma += pary[i][j];
                if(pary[i][j] == -1)
                {
                    mini = min(mini, suma_pop);
                    suma_pop = suma;
                }
                wynik = max(wynik, suma - mini);
            }
            REP(j, n)
                pary[i][j] *= -1;
            int wynik2 = 0, suma2 = 0, suma_pop2 = 0, mini2 = 1e9;
            REP(j, n)
            {
                suma2 += pary[i][j];
                if(pary[i][j] == -1)
                {
                    mini2 = min(mini2, suma_pop2);
                    suma_pop2 = suma2;
                }
                wynik2 = max(wynik2, suma2 - mini2);
            }
            www = max(wynik, wynik2);
            answ = max(answ, www);
        }
    }

    cout << answ;

}