// 入力フォーマットチェック２
#include<bits/stdc++.h>
using namespace std;

using ll = long long;

#define GETLINE( A ) string A; getline( cin , A ) 
#define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr ) 
#define FOR( VAR , INITIAL , FINAL_PLUS_ONE ) for( remove_const<remove_reference<decltype( FINAL_PLUS_ONE )>::type >::type VAR = INITIAL ; VAR < FINAL_PLUS_ONE ; VAR ++ ) 
#define REPEAT( HOW_MANY_TIMES ) FOR( VARIABLE_FOR_REPEAT , 0 , HOW_MANY_TIMES ) 
#define QUIT return 0 
#define RETURN( ANSWER ) cout << ( ANSWER ) << "\n"; QUIT 

#define STOI( S , N ) ll N = 0; while( S == "" ? false : S.substr( 0 , 1 ) != " " ){ N = N * 10 + stoi( S.substr( 0 , 1 ) ); S = S.substr( 1 ); } 
// #define CHECK_REDUNDANT_INPUT string VARIABLE_FOR_CHECK_REDUNDANT_INPUT = ""; cin >> VARIABLE_FOR_CHECK_REDUNDANT_INPUT; assert( VARIABLE_FOR_CHECK_REDUNDANT_INPUT == "" ); assert( ! cin );
#define CHECK_REDUNDANT_INPUT string VARIABLE_FOR_CHECK_REDUNDANT_INPUT = ""; getline( cin , VARIABLE_FOR_CHECK_REDUNDANT_INPUT ); assert( VARIABLE_FOR_CHECK_REDUNDANT_INPUT == "" ); assert( ! cin );


int main()
{
  UNTIE;
  GETLINE( S );
  STOI( S , N );
  REPEAT( N ){
    GETLINE( Aj );
  }
  CHECK_REDUNDANT_INPUT;
  RETURN( "YES" );
}