Problem:
Score : 200 points

Problem 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?

Constraints

1≤N≤1000

1≤l_i≤r_i≤100000

No seat is occupied by more than one person.

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
l_1 r_1
:
l_N r_N

Output

Print the number of people sitting at the theater.

Sample Input 1

1
24 30

Sample Output 1

7

There are 7 people, sitting at Seat 24,25,26,27,28,29 and 30.

Sample Input 2

2
6 8
3 3

Sample Output 2

4

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

// #define _CRT_SECURE_NO_WARNINGS
// #define _USE_MATH_DEFINES	// M_PI=3.1415...
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <cmath>
#include <cstdlib>
#include <functional>
#include <locale>
#include <cctype>
#include <sstream>
#include <iomanip>	// 20桁出力 cout << setprecision(20) << double;
#include <queue>
#include <bitset>	// bitset<8> bs1(131uL); // 10000011 bs1[0]は1 01stringからビット集合生成可
using namespace std;

typedef long long LL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<LL> VL;
typedef map<int, int> MAPII;
typedef multimap<int, char, greater<int> > MuMAPIC;
typedef vector<pair<int, int> > VPII;
typedef multimap<int, string, greater<int> > MuMIS;
typedef pair<int, int> P;
typedef pair<int, pair<P, P> > PP;

#define INF 999999999999999997;
#define MP make_pair
#define FAST_IO  cin.tie(0); ios::sync_with_stdio(false);
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define FORL(i,a,b) for(LL i=(a);i<(b);i++)
#define FOR_REV(i,a,b) for(int i=(a);i>=(b);i--)
//for gcc (未test)
// #define FOREACH_IT(it,c) for(typeof(c)::iterator it=(c).begin(); it!=(c).end(); ++it)
//for Visual Studio
#define foreach_it(type,it,c) for(type::iterator it=c.begin(),c_end=c.end();it!=c_end;++it)
#define FOR_ITR(d) for(auto itr=d.begin(),d_end=d.end();itr!=d_end;++itr)	// C++11
// for Debug.
#define DUMP_VVI(b) FOR(i,0,b.size()){FOR(j,0,b[i].size())printf("%d ",b[i][j]);puts("");}
#define D_OUT(str,value) if(dbgF){cout<<str<<" : "<<value<<endl;}
// 入力をpush_back(d)やarray[d]に使う時に1行で書ける
// int INPUT_INT() {int d;cin>>d;return d;}
template<class T>T IN() { T d; cin >> d; return d; }
// 最大公約数（Greatest Common Divisor）
LL gcd(LL a, LL b) { return (b > 0) ? gcd(b, a%b) : a; }
// 最小公倍数（Least Common Multiple）
LL lcm(LL a, LL b) { return a / gcd(a, b) * b; }
// Y年はうるう年か否か
bool uruu(LL Y) { return (((Y % 4 == 0 && Y % 100 != 0) || Y % 400 == 0) ? true : false); }

int dx[4] = { 0,1,0,-1 };
int dy[4] = { 1,0,-1,0 };

// vector注意
// vec[i][j]の形に入力を入れるとき、vecは初期化してある必要がある.

// ------------------- include, typedef, define END. -------------------

int main() {
	FAST_IO;
	// for D_OUT(str, value)  ... cout<< str <<" : "<< value <<endl;
	bool dbgF = true;

	//コードはここから書く.
	LL n,ans=0;
	cin >> n;
	FOR(i, 0, n) {
		LL a, b;
		cin >> a >> b;
		ans += b - a + 1;
	}
	cout << ans << endl;
	return 0;
}