Link

http://acm.hust.edu.cn/vjudge/contest/121539#problem/C

Description

standard input/output 

After a long ACM training day, Master Hasan invited his trainees for a light dinner in the cafeteria. The cafeteria has N tables, each with a number of chairs around it. Before accepting the trainees into the cafeteria, Master Hasan wants to know how many unused chairs are there in the cafeteria. If there isn't enough chairs, he might invite them to a well-known Indian restaurant.

Input

The first line of input contains a single integer N(1 ≤ N ≤ 100), the number of tables in the cafeteria.

Each of the following N lines contains two integers describing a table, A and B(1 ≤ A ≤ B ≤ 100), where A represents the number of used chairs, and B represents the total number of chairs around that table.

Output

Print the number of unused chairs in the cafeteria.

Sample Input

Input

3 1 3 4 4 5 8

Output

5

Solution

This problem is a piece of cake.The number of unused chair of each table is B-A,and our task is to sum them up.

C++ Code

#include<iostream>

using namespace std;

int main()

{

　　int n,a,b,sum;

　　cin>>n;sum=0;

　　while(n--)

　　{

　　　　cin>>a>>b;

　　　　sum+=b-a;

　　}

　　cout<<sum<<endl;

　　return 0;

}