#include <cstdio>
#include <cstring>

#define NMax 505

using namespace std;

char String[NMax];
short N, DP[NMax][NMax], MaxS;
short AI[3*NMax][27];

inline short Max (short a, short b)
{
    if (a>b)
    {
        return a;
    }
    return b;
}

void Read ()
{
    freopen ("palm.in", "r", stdin);
    scanf ("%s", String);
    N=(short)strlen (String);
}

void Update (short K, short L, short R, short P, short C, short V)
{
    short Mid=(L+R)>>1;
    if (L==R)
    {
        for (short c=C; c>=0; --c)
        {
            AI[K][c]=Max (AI[K][c], V);
        }
        return;
    }
    if (P<=Mid)
    {
        Update (K<<1, L, Mid, P, C, V);
    }
    else
    {
        Update ((K<<1)+1, Mid+1, R, P, C, V);
    }
    for (short c=0; c<=26; ++c)
    {
        AI[K][c]=Max (AI[K<<1][c], AI[(K<<1)+1][c]);
    }
}

short Query (short K, short L, short R, short Q, short V)
{
    short Mid=(L+R)>>1;
    if (R<=Q)
    {
        return AI[K][V];
    }
    if (Q<=Mid)
    {
        return Query (K<<1, L, Mid, Q, V);
    }
    return Max (Query (K<<1, L, Mid, Q, V), Query ((K<<1)+1, Mid+1, R, Q, V));
}

void Solve ()
{
    for (short i=N-1; i>=0; --i)
    {
        DP[i][i]=1;
        for (short j=N-1; j>i; --j)
        {
            if (String[i]!=String[j])
            {
                continue;
            }
            DP[i][j]=2+Query (1, 0, N-1, j-1, (short)String[i]-(short)'a');
            MaxS=Max (MaxS, DP[i][j]);
            Update (1, 0, N-1, j, (short)String[j]-(short)'a', DP[i][j]);
        }
        Update (1, 0, N-1, i, (short)String[i]-(short)'a', DP[i][i]);
    }
}

inline void Print ()
{
    freopen ("palm.out", "w", stdout);
    printf ("%d\n", MaxS);
}

int main()
{
    Read ();
    Solve ();
    Print ();
    return 0;
}