Language: C++

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
#define fo(a,b) for(int a=0;a<b;a++)
#define Sort(a) sort(a.begin(),a.end())
#define rev(a) reverse(a.begin(),a.end())
#define fi first
#define se second
#define co(a) cout<<a<<endl
#define sz size()
#define bgn begin()
#define en end()
#define pb(a) push_back(a)
#define pp() pop_back()
#define V vector
#define P pair
#define V2(a,b,c) V<V<int>> a(b,V<int>(c))
#define V2a(a,b,c,d) V<V<int>> a(b,V<int>(c,d))
#define incin(a) int a; cin>>a
#define yuko(a) setprecision(a)
#define uni(a) a.erase(unique(a.begin(),a.end()),a.end())
#define pri priority_queue
#define syo <int,V<int>
#define ff fi.fi
#define fs fi.se
#define sf se.fi
#define ss se.se
#define all(a)  (a).begin(),(a).end()
#define Pi P<int,int>
#define elif else if
//#define min min<int>
//#define max max<int>
int low(V<int> a,int b){
  decltype(a)::iterator c=lower_bound(a.begin(),a.end(),b);
  int d=c-a.bgn;
  return d;
}
int upp(V<int> a,int b){
  decltype(a)::iterator c=upper_bound(a.begin(),a.end(),b);
  int d=c-a.bgn;
  return d;
}
template<class T>
 void cou(vector<vector<T>> a){
  int b=a.size();
  int c=a[0].size();
  fo(i,b){
    fo(j,c){
      cout<<a[i][j];
      if(j==c-1)
        cout<<endl;
      else
        cout<<' ';
    }
  }
}
/*template<>
 void cou(vector<vector<char>> a){
  int b=a.size();
  int c=a[0].size();
  fo(i,b){
    fo(j,c){
      cout<<a[i][j];
      if(j==c-1)
        cout<<endl;
      else
        cout<<' ';
    }
  }
}*/
 int wari(int a,int b) {
   if(a%b==0)
     return a/b;
   else
     return a/b+1;
 }
 int keta(int a){
  double b=a;
  b=log10(b);
  int c=b;
  return c+1;
 }
 int souwa(int a){
  return a*(a+1)/2;
 }
 /*int lcm(int a,int b){
  int d=a,e=b,f;
  if(a<b)
    swap(a,b);
  int c,m=1;
  while(m){
    c=a%b;
    if(c==0){
       f=b;
      m--;
    }
    else{
      a=b;
      b=c;
 }
  }
  return d*e/f;
    } */
int gcm(int a,int b){
  if(a%b==0)
    return b;
  return gcm(b,a%b);
}
 bool prime(int a){
   if(a<2)
     return false;
   else if(a==2)
     return true;
   else if(a%2==0)
     return false;
   double b=sqrt(a);
    for(int i=3;i<=b;i+=2){
      if(a%i==0){
        return false;
      }
    }
   return true;
 }

struct Union{
  vector<int> par;
  Union(int a){
  par= vector<int>(a,-1);
  }
  int find(int a){
    if(par[a]<0)
      return a;
    else
      return par[a]=find(par[a]);
  }
  bool same(int a,int b){
    return find(a)==find(b);
  }
  int Size(int a){
    return -par[find(a)];
  }
  void unite(int a,int b){
    a=find(a);
    b=find(b);
    if(a==b)
      return;
    if(Size(b)>Size(a))
      swap<int>(a,b);
    par[a]+=par[b];
    par[b]=a;
  }
};
int ketas(int a){
  string b=to_string(a);
  int c=0;
  fo(i,keta(a)){
    c+=b[i]-'0';
  }
  return c;
}
/*int gcm(int a,int b){
    if(b==0)
        return a;
    return gcm(b,a%b);
}*/
int lcm(int a,int b){
    return a/gcm(a,b)*b;
}
/*struct aa{
  vector<int> gt;
  aa(int n){
  gt= vector<int>(n, 1);
  }
  void c(V<int> d,int b){
  if(d[b]==0){
    gt[d[b]-1]++;
    gt[gt.sz-1]++;
  }
  else{
    gt[d[b]-1]++;
    c(d,d[d[b]]-1);
  }
}
void cok(int a){
  cout<<gt[a-1]<<endl;
  fo(i,a-1)
  cout<<gt[i]<<endl;
}
};
*/
/*struct dfs(){

}*/
bool fe(int a,int b){
  a%=10;
  b%=10;
  if(a==0)
    a=10;
  if(b==0)
    b=10;
  if(a>b)
    return true;
  else
    return false;
}
int INF=1000000007;
struct edge{int s,t,d; };
V<int> mojisyu(string a){
  V<int> b(26,0);
  fo(i,a.sz){
    b[a[i]-'a']++;
  }
  return b;
}
int wa2(int a){
  if(a%2==1)
    return a/2;
  return a/2-1;
}
/*signed main(){
  int a,b,c;
  cin>>a>>b>>c;
  V<V<edge>> d(a);
  fo(i,b){
    edge e;
    cin>>e.s>>e.t>>e.d;
    d[e.s].pb(e);
  }
  V<int> e(a,INF);
  e[c]=0;
  priority_queue<P<int,int>,V<P<int,int>>,greater<P<int,int>>> f;
  f.push({0,c});
  int h=INF;
  while(!f.empty()){
    P<int,int> g;
    g=f.top();
    f.pop();
    int v = g.second, i = g.first;
    for(edge l : d[v]){
      if(e[l.t] > i + l.d){
        e[l.t] = i + l.d;
        f.push({i+l.d , l.t});
      }
    }
  }
  fo(i,a){
    if(e[i]==INF)
      cout<<"INF"<<endl;
    else
      cout<<e[i]<<endl;
  }
}
?*/
signed main(){
  string a,b,c;
  cin>>a;
  int d=2;
  fo(i,a.sz){
    a.back();
    if(a.sz%2==1)
      continue;
    b=a.substr(a.bgn,a.sz/2);
    c=a.substr(a.bgn+a.sz/2);
    if(b==c){
      d=a.sz;
      break;
    }
  }
  cout<<d<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:260:11: warning: ignoring return value of 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::back() [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&]', declared with attribute 'nodiscard' [-Wunused-result]
  260 |     a.back();
      |     ~~~~~~^~
In file included from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:1:
/usr/include/c++/14/bits/basic_string.h:1350:7: note: declared here
 1350 |       back() noexcept
      |       ^~~~
a.cc:12:18: error: cannot convert 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
   12 | #define bgn begin()
      |                  ^
      |                  |
      |                  std::__cxx11::basic_string<char>::iterator
a.cc:263:18: note: in expansion of macro 'bgn'
  263 |     b=a.substr(a.bgn,a.sz/2);
      |                  ^~~
/usr/include/c++/14/bits/basic_string.h:3208:24: note:   initializing argument 1 of 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::substr(size_type, size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 3208 |       substr(size_type __pos = 0, size_type __n = npos) const
      |              ~~~~~~~~~~^~~~~~~~~
a.cc:264:21: error: cannot convert '__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
  264 |     c=a.substr(a.bgn+a.sz/2);
      |                ~~~~~^~~~~~~
      |                     |
      |                     __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >
/usr/include/c++/14/bits/basic_string.h:3208:24: note:   initializing argument 1 of 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::substr(size_type, size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 3208 |       substr(size_type __pos = 0, size_type __n = npos) const
      |              ~~~~~~~~~~^~~~~~~~~