#include <bits/stdc++.h>

using namespace std;
ifstream fin("palm.in");
ofstream fout("palm.out");
int n,d[501][501];
string s;
char lit;
int main()
{
    fin>>s;
    n=s.size();
    int last=0;
    int i;
    for(lit='z'; lit>='a'; lit--)
    {
        int ok = 0;
        for(i=0; i<=n; i++)
            if(s[i] == lit)
                d[i][i] = 1, ok = 1;
        if (ok)
        {
            for(int len=2; len<=n; len++)
                for(i=0; i+len-1<n; i++)
                {
                    d[i][i+len-1] = max(d[i][i+len-1], max(d[i+1][i+len-1], d[i][i+len-1-1]));
                    if(s[i] == s[i+len-1] && s[i] == lit)
                        d[i][i+len-1] = max(d[i][i+len-1], d[i+1][i+len-2] + 2);
                }
        }
    }
    fout<<d[0][n-1];
    return 0;
}