public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] A = new int [ 101 ] ;
  int l1 = sc . nextInt ( ) ;
  int r1 = sc . nextInt ( ) ;
  for ( int i = l1 ;
  i < r1 ;
  i ++ ) {
    A [ i ] = 1 ;
  }
  for ( int i = 0 ;
  i < n - 1 ;
  i ++ ) {
    int x = sc . nextInt ( ) ;
    int y = sc . nextInt ( ) ;
    for ( int j = x ;
    j < y ;
    j ++ ) {
      A [ j ] = 2 ;
    }
  }
  int count = 0 ;
  for ( int i = 0 ;
  i <= 100 ;
  i ++ ) {
    if ( A [ i ] == 1 ) {
      count ++ ;
    }
  }
  System . out . println ( count ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] A = new int [ 101 ] ; int l1 = sc . nextInt ( ) ; int r1 = sc . nextInt ( ) ; for ( int i = l1 ; i < r1 ; i ++ ) { A [ i ] = 1 ; } for ( int i = 0 ; i < n - 1 ; i ++ ) { int x = sc . nextInt ( ) ; int y = sc . nextInt ( ) ; for ( int j = x ; j < y ; j ++ ) { A [ j ] = 2 ; } } int count = 0 ; for ( int i = 0 ; i <= 100 ; i ++ ) { if ( A [ i ] == 1 ) { count ++ ; } } System . out . println ( count ) ; }
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