#include <iostream> #include <map> using namespace std; #define int long long const int N = 3<<17; int ph[N], sh[N], pw[N], mod = 1e9 + 9, Ans; map<int, int> cnt[N], prv; int get1(int l, int r){ return (ph[r] - ph[--l] * pw[r - l] % mod + mod) % mod; } int get2(int l, int r){ return (sh[l] - sh[++r] * pw[r - l] % mod + mod) % mod; } signed main(){ string s; cin>>s; int n = s.size(); for (int i=1;i<=n;i++) ph[i] = (ph[i-1] * 256 + s[i-1]) % mod; for (int i=n;i>=1;i--) sh[i] = (sh[i+1] * 256 + s[i-1]) % mod; for (int i=pw[0]=1;i<=n;i++) pw[i] = pw[i-1] * 256 % mod; for (int i=1;i<=n;i++){ int l = 0, r = min(i, n - i + 1) + 1, h, hh; while (l + 1 < r){ int mid = (l + r) / 2; if (get1(i - mid + 1, i) == get2(i, i + mid - 1)) l = mid; else r = mid; } /////////////////////////////////////////////////// h = get1(i - l + 1, i); cnt[l + l - 1][h]++; while (l >= 1 and prv.find(h) == prv.end()){ l--; hh = get1(i - l + 1, i); prv[h] = hh, h = hh; } ////////////////////////////////////////////////// l = 0, r = min(i - 1, n - i + 1) + 1; while (l + 1 < r){ int mid = (l + r) / 2; if (get1(i - mid, i-1) == get2(i, i + mid - 1)) l = mid; else r = mid; } ////////////////////////////////////////////////// h = get1(i - l, i - 1); cnt[l + l][h]++; while (l >= 1 and prv.find(h) == prv.end()){ l--; hh = get1(i - l, i - 1); prv[h] = hh, h = hh; } } for (int i=n;i>=1;i--){ for (auto [j, k] : cnt[i]){ Ans = max(Ans, i * k); if (i - 2 > 0) cnt[i - 2][prv[j]] += k; } } cout<<Ans<<'\n'; }