Language: C++

// template
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<long long, long long> LP;
#define INF 999999999
#define MOD 1000000007
#define REP(i, n) for(int i = 0, i##_len = (n); i < i##_len; ++i)
#define REP_AB(i, a, b) for (int i = int(a); i <= int(b); ++i)
#define ALL(v) v.begin(), v.end()
#define SORT(v) sort(ALL(v))
#define UNIQUE(v) sort(ALL(v));v.erase(unique(ALL(v)), v.end());
#define SIZE(x) ((ll)(x).size())
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return (a / gcd(a, b)) * b;}
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
#define out cout
#define in cin
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
// template end


int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    string s;
    in >> s;
    ll ans = 0;
    REP(i, s.size()){
        if(i % 2 == 1) continue;
        if(i < 2) continue;
        bool even = true;
        REP(j, i / 2){
            if s[j] != s[i/2 + j]{
                even = false;
            }
        }
        if(even){
            ans = max(ans, i);
        }
    }
    out << ans << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:38:16: error: expected '(' before 's'
   38 |             if s[j] != s[i/2 + j]{
      |                ^
      |                (
a.cc:43:22: error: no matching function for call to 'max(ll&, int&)'
   43 |             ans = max(ans, i);
      |                   ~~~^~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:43:22: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   43 |             ans = max(ans, i);
      |                   ~~~^~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:43:22: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   43 |             ans = max(ans, i);
      |                   ~~~^~~~~~~~