#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
char v[505];
int a[505][505];
int main()
{
    int n,rez,i,j,l;
    char c;
    freopen("palm.in","r",stdin);
    freopen("palm.out","w",stdout);
    gets(v);
    n=strlen(v)-1;
    for(c='z'; c>='a'; c--)
    {
        for(i=0; i<=n; i++)
            if(v[i]==c)
                a[i][i]=1;
        for(i=0; i<n; i++)
            if(v[i]==v[i+1] && v[i]==c)
                a[i][i+1]=2;
        for(l=2; l<=n; l++)
            for(i=0; i+l<=n; i++)
            {
                j=i+l;
                if(v[i]==v[j] && v[i]==c)
                    a[i][j]=a[i+1][j-1]+2;
                else
                {
                    a[i][j]=max(a[i][j],a[i+1][j]);
                    a[i][j]=max(a[i][j],a[i][j-1]);
                }
            }
    }
    printf("%d",a[0][n]);

    return 0;
}