#include <bits/stdc++.h>
using namespace std;

const int DIM = 505;
const int SGM = 26;

int dp[DIM][DIM], nxt[DIM][SGM], prv[DIM][SGM];
char str[DIM];

int main(void) {
    freopen("palm.in", "r", stdin);
    freopen("palm.out", "w", stdout);
    int n;
    cin >> (str + 1);
    n = strlen(str + 1);
    for (int i = 1; i <= n; ++i) {
        for (int c = 0; c <= 25; ++c)
            prv[i][c] = prv[i - 1][c];
        prv[i][str[i] - 'a'] = i;
    }
    for (int c = 0; c <= 25; ++c)
        nxt[n + 1][c] = n + 1;
    for (int i = n; i >= 1; --i) {
        for (int c = 0; c <= 25; ++c)
            nxt[i][c] = nxt[i + 1][c];
        nxt[i][str[i] - 'a'] = i;
    }
    int ans = 0;
    for (int i = n; i >= 1; --i) {
        for (int j = i; j <= n; ++j) {
            if (i == j)
                dp[i][j] = 1;
            else if (i != j && str[i] == str[j]) {
                dp[i][j] = 2;
                for (int c = str[i] - 'a'; c <= 25; ++c) {
                    int p = nxt[i + 1][c], q = prv[j - 1][c];
                    if (p <= q && p <= j && i <= q)
                        dp[i][j] = max(dp[i][j], dp[p][q] + 2);
                }
            }
            ans = max(ans, dp[i][j]);
        }
    }
    cout << ans;
    return 0;
}