#include <cstdio>
#include <algorithm>
#include <cstring>
#define maxN 502
#define maxC 26
using namespace std;
int n, i, j;
char s[maxN];
int dp[maxN][maxN], pos[maxC][maxN];
void read()
{
    freopen("palm.in", "r", stdin);
    gets(s + 1);
    n = strlen(s + 1);
}
void solve()
{
    int i, j, k;
    for (k = 0; k < maxC; ++ k)
        for (i = 1; i <= n; ++ i)
            if (s[i] - 'a' == k)
               pos[k][i] = i;
          else
               pos[k][i] = pos[k][i - 1];

    for (k = 'z' - 'a'; k >= 0; -- k)
    {
        for (i = n; i >= 1; -- i)
            for (j = i; j <= n; ++ j)
        {
            if (i == j && s[i] == k + 'a')
                dp[i][j] = 1;
            else
                if (i != j && pos[k][j] > i)
                {
                    dp[i][j] = max(dp[i][j], max(dp[i][j - 1], dp[i + 1][j]));
                    if (s[i] == k + 'a')
                       dp[i][j] = max(dp[i][j], dp[i + 1][pos[k][j] - 1] + 2);
                }
        }
    }
}
void write()
{
    freopen("palm.out", "w", stdout);
    printf("%d", dp[1][n]);
}
int main()
{
    read();
    solve();
    write();
    return 0;
}