#include using namespace std; struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star; #define all(c) (c).begin(), (c).end() #define rall(c) (c).rbegin(), (c).rend() #define vv(type, c, m, n, i) vector> c(m, vector(n, i)) #define mat(type, c, m, n) vector> c(m, vector(n));for(auto& r:c)for(auto& i:r)cin>>i; #define rep(i,a,n) for(int i=(a), i##_len=(n); ii##_len; --i) #define each(x,y) for(auto &(x):(y)) #define var(type, ...)type __VA_ARGS__;Scan(__VA_ARGS__); template void Scan(T& t) { cin >> t; } templatevoid Scan(First& first, Rest&...rest) { cin >> first; Scan(rest...); } #define vec(type, c, n) vector c(n);for(auto& i:c) cin>>i; #define len(x) ((int)(x).size()) #define mp make_pair #define eb emplace_back #define em emplace #define pb pop_back #define fi first #define se second #define get(a, i) get(a) #define mt make_tuple #define zero(a, b) setw(a)< vi; typedef vector vd; typedef vector vll; typedef vector vs; typedef vector vb; typedef pair pii; #define mini min_element #define maxi max_element #define sum accumulate #define chmax(a,b) if(ab)a=b template inline void print(T t){cout << t << "\n";} template inline void print(H h, T... t){cout << h << " ";print(t...);} int solve() { var(string, s); int ans = 1; int len_s = len(s); rep(i, 0, len_s - 1) { int h = len_s; while (true) { int r = s.rfind(s[i], h - 1); if (i == r) break; h = r; int cnt = 0; int j = i; while (j < r) { if(s[j] == s[r]) cnt += 2; ++j; --r; } chmax(ans, cnt + (j == r)); } } return ans; } int main() { print(solve()); return 0; }