#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <numeric>
#include <bitset>
#include <complex>
#define rep(x, to) for (int x = 0; x < (to); x++)
#define REP(x, a, to) for (int x = (a); x < (to); x++)
#define foreach(itr, x) for (typeof((x).begin()) itr = (x).begin(); itr != (x).end(); itr++)
#define EPS (1e-14)

using namespace std;

typedef long long ll;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef complex<double> Complex;
typedef vector< vector<int> > Mat;


int ans;
string s;
int dp[55][55];
int dp2[55];

void solve() {
	for (int i = 0; i < s.size(); i++) {
		dp[i][i] = 1;
	}
	for (int i = s.size() - 1; i >= 0; i--) {
		for (int j = i + 1; j < s.size(); j++) {
			if (s[i] == s[j]) {
				if (i + 1 > j - 1) dp[i][j] = 2;
				if (i + 1 <= j - 1 && dp[i + 1][j - 1] > 0) {
					dp[i][j] = dp[i + 1][j - 1] + 2;
				}
			} else {
				dp[i][j] = 0;
			}
		}
	}
#if 0
	rep(i, s.size()) {
		rep(j, s.size()) {
			cout << dp[i][j] << " ";
		}
		cout << endl;
	}
#endif
	for (int i = 0; i < s.size(); i++) {
		for (int j = i; j > 0; j--) {
			if (dp[j][i] > 0) {
				if (j - 1 >= 0) {
					dp2[i] = max(dp2[i], max(dp[j][i], dp2[j - 1]));
				} else {
					dp2[i] = max(dp2[i], dp[j][i]);
				}
			}
		}
	}
	cout << dp2[s.size() - 1] << endl;
}

int main() {
	cin >> s;
	solve();
	return 0;
}