#include <bits/stdc++.h>
using namespace std;
ifstream fin ("palm.in");
ofstream fout("palm.out");
int n,i,j,dim,sol;
int D[510][510];
char s[510],ch;
int main(){
    fin>>s+1;
    n=strlen(s+1);
    for(ch='z';ch>='a';ch--){
        for(dim=2;dim<=n;dim++){
            for(i=1;i<=n-dim+1;i++){
                j=i+dim-1;
                if(s[i]==ch){
                    D[i][i]=1;
                    if(s[i]==s[j])
                        D[i][j]=max(D[i][j],2+D[i+1][j-1]);
                }
                D[i][j]=max(D[i][j],max(D[i+1][j],D[i][j-1]));
                sol=max(sol,D[i][j]);
            }
        }
    }
    fout<<sol;
    return 0;
}