public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] a = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    a [ i ] = sc . nextInt ( ) ;
  }
  sc . close ( ) ;
  boolean nodec = true ;
  for ( int i = 1 ;
  i < n ;
  i ++ ) {
    if ( a [ i ] <= a [ i - 1 ] ) nodec = false ;
  }
  if ( nodec ) {
    System . out . println ( 1 ) ;
    return ;
  }
  int m = 500 ;
  int l = 1 , r = 210000 ;
  int mid = 2 ;
  int [ ] dec = new int [ m ] ;
  out : while ( r - l > 1 ) {
    mid = ( l + r ) / 2 ;
    dec = new int [ m ] ;
    Arrays . fill ( dec , 1 ) ;
    nout : for ( int i = 1 ;
    i < n ;
    i ++ ) {
      if ( a [ i ] <= a [ i - 1 ] && a [ i ] - 1 < m ) {
        if ( dec [ a [ i ] - 1 ] < mid ) {
          dec [ a [ i ] - 1 ] ++ ;
        }
        else {
          int pos = a [ i ] - 1 ;
          while ( pos > 0 ) {
            dec [ pos - 1 ] ++ ;
            for ( int j = pos ;
            j < m ;
            j ++ ) {
              dec [ j ] = 1 ;
            }
            if ( dec [ pos - 1 ] <= mid ) continue nout ;
            pos -- ;
          }
          l = mid ;
          continue out ;
        }
      }
      else {
        for ( int j = a [ i ] - 1 ;
        j < m ;
        j ++ ) {
          dec [ j ] = 1 ;
        }
      }
    }
    r = mid ;
  }
  System . out . println ( r ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] a = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { a [ i ] = sc . nextInt ( ) ; } sc . close ( ) ; boolean nodec = true ; for ( int i = 1 ; i < n ; i ++ ) { if ( a [ i ] <= a [ i - 1 ] ) nodec = false ; } if ( nodec ) { System . out . println ( 1 ) ; return ; } int m = 500 ; int l = 1 , r = 210000 ; int mid = 2 ; int [ ] dec = new int [ m ] ; out : while ( r - l > 1 ) { mid = ( l + r ) / 2 ; dec = new int [ m ] ; Arrays . fill ( dec , 1 ) ; nout : for ( int i = 1 ; i < n ; i ++ ) { if ( a [ i ] <= a [ i - 1 ] && a [ i ] - 1 < m ) { if ( dec [ a [ i ] - 1 ] < mid ) { dec [ a [ i ] - 1 ] ++ ; } else { int pos = a [ i ] - 1 ; while ( pos > 0 ) { dec [ pos - 1 ] ++ ; for ( int j = pos ; j < m ; j ++ ) { dec [ j ] = 1 ; } if ( dec [ pos - 1 ] <= mid ) continue nout ; pos -- ; } l = mid ; continue out ; } } else { for ( int j = a [ i ] - 1 ; j < m ; j ++ ) { dec [ j ] = 1 ; } } } r = mid ; } System . out . println ( r ) ; }
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