#include <cstdio>
#include <cstring>

#define NMax 505

using namespace std;

char String[NMax];
int N, DP[NMax][NMax], MaxS;
int AI[4*NMax][255];

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

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

void Update (int K, int L, int R, int P, int C, int V)
{
    int Mid=(L+R)/2;
    if (L==R)
    {
        for (int c=C; c>=(int)'a'; --c)
        {
            AI[K][c]=Max (AI[K][c], V);
        }
        return;
    }
    if (P<=Mid)
    {
        Update (2*K, L, Mid, P, C, V);
    }
    else
    {
        Update (2*K+1, Mid+1, R, P, C, V);
    }
    for (int c=(int)'a'; c<='z'; ++c)
    {
        AI[K][c]=Max (AI[2*K][c], AI[2*K+1][c]);
    }
}

int Query (int K, int L, int R, int Q, int V)
{
    int Mid=(L+R)/2;
    if (R<=Q)
    {
        return AI[K][V];
    }
    if (Q<=Mid)
    {
        return Query (2*K, L, Mid, Q, V);
    }
    return Max (Query (2*K, L, Mid, Q, V), Query (2*K+1, Mid+1, R, Q, V));
}

void Solve ()
{
    for (int i=N-1; i>=0; --i)
    {
        DP[i][i]=1;
        for (int j=i+1; j<N; ++j)
        {
            if (String[i]!=String[j])
            {
                continue;
            }

            /*DP[i][j]=2;
            for (int ii=i+1; ii<j; ++ii)
            {
                for (int jj=ii; jj<j; ++jj)
                {
                    if (String[ii]!=String[jj])
                    {
                        continue;
                    }
                    if (String[i]<=String[ii] and String[jj]>=String[j])
                    {
                        DP[i][j]=Max (DP[i][j], DP[ii][jj]+2);
                    }
                }
            }*/

            DP[i][j]=2+Query (1, 0, N-1, j-1, (int)String[i]);
            MaxS=Max (MaxS, DP[i][j]);
        }
        for (int j=i; j<N; ++j)
        {
            if (String[i]!=String[j])
            {
                continue;
            }
            Update (1, 0, N-1, j, (int)String[j], DP[i][j]);
        }
    }
}

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

void Test ()
{
    freopen ("palm.in", "w", stdout);
    for (char c='a'; c<='z'; ++c)
    {
        for (int i=1; i<=9; ++i)
        {
            printf ("%c", c);
        }
    }
    for (char c='z'; c>='a'; --c)
    {
        for (int i=1; i<=9; ++i)
        {
            printf ("%c", c);
        }
    }
}

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