static int number_of_ways ( int n ) {
  int [ ] includes_3 = new int [ n + 1 ] ;
  int [ ] not_includes_3 = new int [ n + 1 ] ;
  includes_3 [ 3 ] = 1 ;
  not_includes_3 [ 1 ] = 1 ;
  not_includes_3 [ 2 ] = 2 ;
  not_includes_3 [ 3 ] = 3 ;
  for ( int i = 4 ;
  i <= n ;
  i ++ ) {
    includes_3 [ i ] = includes_3 [ i - 1 ] + includes_3 [ i - 2 ] + not_includes_3 [ i - 3 ] ;
    not_includes_3 [ i ] = not_includes_3 [ i - 1 ] + not_includes_3 [ i - 2 ] ;
  }
  return includes_3 [ n ] ;
}

static int number_of_ways ( int n ) { int [ ] includes_3 = new int [ n + 1 ] ; int [ ] not_includes_3 = new int [ n + 1 ] ; includes_3 [ 3 ] = 1 ; not_includes_3 [ 1 ] = 1 ; not_includes_3 [ 2 ] = 2 ; not_includes_3 [ 3 ] = 3 ; for ( int i = 4 ; i <= n ; i ++ ) { includes_3 [ i ] = includes_3 [ i - 1 ] + includes_3 [ i - 2 ] + not_includes_3 [ i - 3 ] ; not_includes_3 [ i ] = not_includes_3 [ i - 1 ] + not_includes_3 [ i - 2 ] ; } return includes_3 [ n ] ; }
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