#include <fstream>
#include <cstring>
using namespace std;

ifstream fin("palm.in");
ofstream fout("palm.out");

char c[510],x;
int n,i,j,lung,d[510][510],sol;

int main(){
    fin>>c+1;
    n=strlen(c+1);

    for(x='z';x>='a';x--){
        for(lung=2;lung<=n;lung++){
            for(i=1;i+lung-1<=n;i++){
                if(c[i]==x){
                    d[i][i]=1;

                    j=i+lung-1;
                    if(c[i]==c[j])
                        d[i][j]=max(d[i][j],d[i+1][j-1]+2);
                }

                d[i][j]=max(d[i][j], max(d[i+1][j],d[i][j-1]));
            }
        }
    }

    fout<<d[1][n];

    return 0;
}