public static void main ( String [ ] args ) {
  FastReader sc = new FastReader ( ) ;
  int n = sc . nextInt ( ) ;
  int a = sc . nextInt ( ) ;
  int [ ] arr = new int [ n - 1 ] ;
  for ( int i = 0 ;
  i < arr . length ;
  i ++ ) {
    arr [ i ] = sc . nextInt ( ) ;
  }
  Arrays . sort ( arr ) ;
  int count = 0 ;
  while ( arr [ arr . length - 1 ] >= a ) {
    arr [ arr . length - 1 ] -- ;
    a ++ ;
    count ++ ;
    Arrays . sort ( arr ) ;
  }
  System . out . println ( count ) ;
}

public static void main ( String [ ] args ) { FastReader sc = new FastReader ( ) ; int n = sc . nextInt ( ) ; int a = sc . nextInt ( ) ; int [ ] arr = new int [ n - 1 ] ; for ( int i = 0 ; i < arr . length ; i ++ ) { arr [ i ] = sc . nextInt ( ) ; } Arrays . sort ( arr ) ; int count = 0 ; while ( arr [ arr . length - 1 ] >= a ) { arr [ arr . length - 1 ] -- ; a ++ ; count ++ ; Arrays . sort ( arr ) ; } System . out . println ( count ) ; }
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