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1111.cpp
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1111.cpp
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#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fr(i,j,k) for(int i=j;i<k;i++)
#define f(n) fr(i,0,n)
#define f1(n) fr(i,1,n+1)
#define pb push_back
#define F first
#define S second
#define all(x) x.begin(), x.end()
const int mod = 1e9 + 7;
const int maxn = 2000005;
vector<char>v;
string manacher(string ss) {
v.pb('*');
for (auto &i : ss) {
v.pb('#');
v.pb(i);
}
v.pb('#');
int dp[v.size()] = {};
int mx = 0, id = 0;
for (int i = 0 ; i < v.size() ; i++) {
dp[i] = mx > i ? min(dp[2*id-i], mx - i) : 1;
while(v[i + dp[i]] == v[i - dp[i]]) {
dp[i]++;
}
if (i + dp[i] > mx) {
id = i;
mx = i + dp[i];
}
}
int ans = 0;
for (int i = 0 ; i < v.size() ; i++) {
if (dp[i] > dp[ans]) {
ans = i;
}
}
string ret;
for (int i = ans - dp[ans] + 1 ; i < ans + dp[ans] ; i++) {
if (v[i] >= 'a' && v[i] <= 'z') {
ret += v[i];
}
}
return ret;
}
void solve() {
string s;
cin >> s;
cout << manacher(s) << '\n';
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int c = 0;
int t;
if (!c) {
t = 1;
}
else {
cin >> t;
}
while (t--) {
solve();
}
}