#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

#define maxn 510
#define maxs 27

int n;
char s[maxn];
int d[maxn][maxn][maxs];

int main()
{
    freopen("palm.in", "r", stdin);
    freopen("palm.out", "w", stdout);

    scanf("%s", s+1);
    n=strlen(s+1);
    for(int i=1; i<=n; ++i)
    {
        s[i]-='a';
        d[i][i][s[i]]=1;
    }

    for(int i=1; i<=n; ++i)
        for(int j=1; j+i-1<=n; ++j)
        {
            if(s[j]==s[i+j-1] && i!=1)
                d[j][i+j-1][s[j]]=d[j+1][i+j-2][s[j]]+2;
            for(int k=25; k>=0; --k)
                d[j][i+j-1][k]=max(max(d[j][i+j-1][k], d[j][i+j-1][k+1]), max(d[j][i+j-2][k], d[j+1][i+j-1][k]));
        }

    printf("%d\n", d[1][n][0]);

    return 0;
}