// 愚直（O((log N)N 2^N)）解チェック
#ifdef DEBUG
  #define _GLIBCXX_DEBUG
  #define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr ); signal( SIGABRT , &AlertAbort )
  #define DEXPR( LL , BOUND , VALUE , DEBUG_VALUE ) CEXPR( LL , BOUND , DEBUG_VALUE )
  #define CERR( MESSAGE ) cerr << MESSAGE << endl;
  #define COUT( ANSWER ) cout << "出力： " << ANSWER << endl
  #define ASSERT( A , MIN , MAX ) CERR( "ASSERTチェック： " << ( MIN ) << ( ( MIN ) <= A ? "<=" : ">" ) << A << ( A <= ( MAX ) ? "<=" : ">" ) << ( MAX ) ); assert( ( MIN ) <= A && A <= ( MAX ) )
#else
  #pragma GCC optimize ( "O3" )
  #pragma GCC optimize( "unroll-loops" )
  #pragma GCC target ( "sse4.2,fma,avx2,popcnt,lzcnt,bmi2" )
  #define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr )
  #define DEXPR( LL , BOUND , VALUE , DEBUG_VALUE ) CEXPR( LL , BOUND , VALUE )
  #define CERR( MESSAGE ) 
  #define COUT( ANSWER ) cout << ANSWER << "\n"
  #define ASSERT( A , MIN , MAX ) assert( ( MIN ) <= A && A <= ( MAX ) )
#endif
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define MAIN main
#define TYPE_OF( VAR ) decay_t<decltype( VAR )>
#define CEXPR( LL , BOUND , VALUE ) constexpr LL BOUND = VALUE
#define CIN( LL , A ) LL A; cin >> A
#define SET_ASSERT( A , MIN , MAX ) cin >> A; ASSERT( A , MIN , MAX )
#define CIN_ASSERT( A , MIN , MAX ) TYPE_OF( MAX ) A; SET_ASSERT( A , MIN , MAX )
#define FOR( VAR , INITIAL , FINAL_PLUS_ONE ) for( TYPE_OF( FINAL_PLUS_ONE ) VAR = INITIAL ; VAR < FINAL_PLUS_ONE ; VAR ++ )
#define QUIT return 0
#define RETURN( ANSWER ) COUT( ( ANSWER ) ); QUIT

#ifdef DEBUG
  inline void AlertAbort( int n ) { CERR( "abort関数が呼ばれました。assertマクロのメッセージが出力されていない場合はオーバーフローの有無を確認をしてください。" ); }
#endif

int MAIN()
{
  UNTIE;
  DEXPR( int , bound_N , 100000 , 100 ); // 0が5個
  CIN_ASSERT( N , 1 , bound_N );
  CEXPR( ll , bound_M , 1000000000000000000 ); // 0が18個
  CIN_ASSERT( M , 2 , bound_M );
  ll LR[bound_N][2];
  FOR( i , 0 , N ){
    CIN_ASSERT( Li , 1 , M );
    CIN_ASSERT( Ri , Li + 1 , M );
    auto& LRi = LR[i];
    LRi[0] = --Li;
    LRi[1] = --Ri;
  }
  int answer = 0;
  ll S = -1;
  while( ( ++S ) >> N == 0 ){
    set<ll> fall{};
    FOR( i , 0 , N ){
      fall.insert( LR[i][(S>>i)&1] );
    }
    int temp = fall.size();
    answer < temp ? answer = temp : answer;
  }
  RETURN( answer );
}