output_description: Print the number of people sitting at the theater.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      l_1 r_1
      :
      l_N r_N
attempt: N=int(input())
  sum=0
  for i range(N):
    l, r =map(int,input().split())
  
problem_description: Statement
  
  Joisino is working as a receptionist at a theater.
  
  The theater has 100000 seats, numbered from 1 to 100000.
  
  According to her memo, N groups of audiences have come so far, and the i-th
  group occupies the consecutive seats from Seat l_i to Seat r_i (inclusive).
  
  How many people are sitting at the theater now?
samples: [{"input": "1\n    24 30", "output": "7\n    \n\nThere are 7 people, sitting at Seat 24,25,26,27,28,29 and 30.\n\n* * *"}, {"input": "2\n    6 8\n    3 3", "output": "4"}]