#include <bits/stdc++.h> #include <map> #include <math.h> #include <algorithm> using namespace std; #define ll long long #define st string #define vt vector #define db long double #define f0(i, n) for (ll i = 0; i < n; i++) int main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); st s; cin >> s; st z = s; reverse(z.begin(), z.end()); ll n = s.size(); ll f[n + 10][n + 10]; s = "0" + s; z = "1" + z; // cout<<s<<" "<<z; for (ll i = 0; i <= n; i++) { f[i][0] = f[0][i] = 0; } // cout<<endl<<s[s.size()]<<" "<<z[z.size()]<<endl; for (ll i = 1; i <= n; i++) { for (ll e = 1; e <= n; e++) { if (s[i] == z[e]) { f[i][e] = f[i - 1][e - 1] + 1; } else { f[i][e] = max(f[i - 1][e], f[i][e - 1]); } // cout<<f[i][e]<<" "; } // cout<<endl; } cout << f[n][n]; }