Language: C++

///   BISMILLAHIR RAHMANIR RAHEEM
///   ALLAH IS WATCHING ME
///   ALLAH save us from COVID-19.Amin.

///   Every soul shall taste death.

///   Tag ::

#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>

///  order_of_key return number of elements less than x.
///  find_by_order return index.

using namespace std;
using namespace __gnu_pbds;


#define MOHAMMAD  ios::sync_with_stdio(0);cin.tie(0);
#define all(x)    (x).begin(), (x).end()
#define AE        cout << fixed << setprecision(2);

/// faster.
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")

int dx8[] = {0, 0, 1, 1, 1, -1, -1, -1}; // 8-direction.......
int dy8[] = {1,-1, 1, -1, 0, 0, -1, 1};
int dx4[]= {1,-1,0,0}; // 4-direction...........
int dy4[]= {0,0,1,-1};

using ll = long long;
const ll MOD = 1e9 + 7;

typedef tree< int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
typedef tree<pair<int, int>,null_type,less<pair<int, int>>,rb_tree_tag,tree_order_statistics_node_update> ordered_multiset;

//debug
template<typename F,typename S>ostream&operator<<(ostream&os,const pair<F,S>&p){return os<<"("<<p.first<<", "<<p.second<<")";}
template<typename T>ostream&operator<<(ostream&os,const vector<T>&v){os<<"{";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<", ";os<<*it;}return os<<"}";}
template<typename T>ostream&operator<<(ostream&os,const set<T>&v){os<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<",";os<<*it;}return os<<"]";}
template<typename T>ostream&operator<<(ostream&os,const multiset<T>&v) {os<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<", ";os<<*it;}return os<<"]";}
template<typename F,typename S>ostream&operator<<(ostream&os,const map<F,S>&v){os<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<", ";os<<it->first<<" = "<<it->second;}return os<<"]";}
#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)
void faltu(){cerr << endl;}
template<typename T>void faltu(T a[],int n){for(int i=0;i<n;++i)cerr<<a[i]<<' ';cerr<<endl;}
template<typename T,typename...hello>void faltu(T arg,const hello&...rest){cerr<<arg<<' ';faltu(rest...);}
//#else
//#define dbg(args...)

/// Modular arithmetic
inline void normal(ll &a) { a %= MOD; (a < 0) && (a += MOD); }
inline ll modMul(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a*b)%MOD; }
inline ll modAdd(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a+b)%MOD; }
inline ll modSub(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); a -= b; normal(a); return a; }
inline ll modPow(ll b, ll p) { ll r = 1; while(p) { if(p&1) r = modMul(r, b); b = modMul(b, b); p >>= 1; } return r; }
inline ll modInverse(ll a) { return modPow(a, MOD-2); }  /// When MOD is prime.
inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }

//***********************************************  The END **********************************************************************************************************************************
const ll N = 2e5;
const ll INF = 1e15;
const ll limit = (1LL<<64) - 1;

ll cc = 0;
vector < ll > e[N+1];
bool visit[N+1];

map <  pair < ll , ll > , ll > mp;

void dfs ( ll node ){
    visit[node] = 1;
    cc++;
    //dbg ( node );
   // dbg ( e[node].size() );
    for ( auto child : e[node] ){
        // dbg ( child );
         if ( visit[child] ) continue;
         dfs ( child );
    }
}

int main()
{

  MOHAMMAD

  ll n , m , u , v;
  cin >> n >> m;
  ll mx = 0;
  while ( m-- ){
       cin >> u >> v;
       if  ( mp[ { u , v } ] or mp[ { v , u } ] ) continue;
       e[u].push_back ( v );
       e[v].push_back ( u );
       mp[ { u , v } ] = 1;
  }

  for ( ll i = 1 ; i<=n ; i++ ){
        if ( visit[i] ) continue;
       // dbg ( cc );
        dfs ( i );
        mx = max ( mx,  cc );
        cc = 0;
  }

  cout << mx  << "\n";




}


/*

Explanation:



TODO :

  Alhamdulillah
*/


Compiler output:
a.cc:65:22: warning: left shift count >= width of type [-Wshift-count-overflow]
   65 | const ll limit = (1LL<<64) - 1;
      |                   ~~~^~~~
a.cc: In function 'void dfs(ll)':
a.cc:74:5: error: reference to 'visit' is ambiguous
   74 |     visit[node] = 1;
      |     ^~~~~
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:80,
                 from a.cc:9:
/usr/include/c++/14/variant:1855:5: note: candidates are: 'template<class _Visitor, class ... _Variants> constexpr std::__detail::__variant::__visit_result_t<_Visitor, _Variants ...> std::visit(_Visitor&&, _Variants&& ...)'
 1855 |     visit(_Visitor&& __visitor, _Variants&&... __variants)
      |     ^~~~~
a.cc:69:6: note:                 'bool visit [200001]'
   69 | bool visit[N+1];
      |      ^~~~~
a.cc:80:15: error: reference to 'visit' is ambiguous
   80 |          if ( visit[child] ) continue;
      |               ^~~~~
/usr/include/c++/14/variant:1855:5: note: candidates are: 'template<class _Visitor, class ... _Variants> constexpr std::__detail::__variant::__visit_result_t<_Visitor, _Variants ...> std::visit(_Visitor&&, _Variants&& ...)'
 1855 |     visit(_Visitor&& __visitor, _Variants&&... __variants)
      |     ^~~~~
a.cc:69:6: note:                 'bool visit [200001]'
   69 | bool visit[N+1];
      |      ^~~~~
a.cc: In function 'int main()':
a.cc:102:14: error: reference to 'visit' is ambiguous
  102 |         if ( visit[i] ) continue;
      |              ^~~~~
/usr/include/c++/14/variant:1855:5: note: candidates are: 'template<class _Visitor, class ... _Variants> constexpr std::__detail::__variant::__visit_result_t<_Visitor, _Variants ...> std::visit(_Visitor&&, _Variants&& ...)'
 1855 |     visit(_Visitor&& __visitor, _Variants&&... __variants)
      |     ^~~~~
a.cc:69:6: note:                 'bool visit [200001]'
   69 | bool visit[N+1];
      |      ^~~~~