public static void main ( String [ ] args ) {
  int count = 0 ;
  int count1 = 0 ;
  int count2 = 0 ;
  int count3 = 0 ;
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] arr = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    arr [ i ] = sc . nextInt ( ) ;
  }
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( arr [ i ] == 4 ) {
      arr [ i ] = 0 ;
      count ++ ;
    }
  }
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( arr [ i ] == 3 ) {
      count3 ++ ;
    }
  }
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( arr [ i ] == 2 ) {
      count2 ++ ;
    }
  }
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( arr [ i ] == 1 ) {
      count1 ++ ;
    }
  }
  if ( count3 > count1 ) {
    count = count1 + count ;
    count3 = count3 - count1 ;
    count1 = 0 ;
    count = count + count1 ;
    count = count + count3 ;
    count3 = 0 ;
    count1 = 0 ;
  }
  else {
    count = count3 + count ;
    count1 = count1 - count3 ;
    count3 = 0 ;
  }
  count = ( count2 / 2 ) + count ;
  if ( count2 % 2 != 0 ) {
    if ( count1 < 3 ) {
      count ++ ;
      count1 = 0 ;
      count2 = 0 ;
    }
    else {
      count1 = count1 - 2 ;
      count ++ ;
      count2 = 0 ;
    }
  }
  count = count + ( count1 / 4 ) ;
  if ( count1 % 4 > 0 ) {
    count ++ ;
  }
  System . out . println ( count ) ;
}

public static void main ( String [ ] args ) { int count = 0 ; int count1 = 0 ; int count2 = 0 ; int count3 = 0 ; Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] arr = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { arr [ i ] = sc . nextInt ( ) ; } for ( int i = 0 ; i < n ; i ++ ) { if ( arr [ i ] == 4 ) { arr [ i ] = 0 ; count ++ ; } } for ( int i = 0 ; i < n ; i ++ ) { if ( arr [ i ] == 3 ) { count3 ++ ; } } for ( int i = 0 ; i < n ; i ++ ) { if ( arr [ i ] == 2 ) { count2 ++ ; } } for ( int i = 0 ; i < n ; i ++ ) { if ( arr [ i ] == 1 ) { count1 ++ ; } } if ( count3 > count1 ) { count = count1 + count ; count3 = count3 - count1 ; count1 = 0 ; count = count + count1 ; count = count + count3 ; count3 = 0 ; count1 = 0 ; } else { count = count3 + count ; count1 = count1 - count3 ; count3 = 0 ; } count = ( count2 / 2 ) + count ; if ( count2 % 2 != 0 ) { if ( count1 < 3 ) { count ++ ; count1 = 0 ; count2 = 0 ; } else { count1 = count1 - 2 ; count ++ ; count2 = 0 ; } } count = count + ( count1 / 4 ) ; if ( count1 % 4 > 0 ) { count ++ ; } System . out . println ( count ) ; }
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