#include <bits/stdc++.h>

using namespace std;

#define REP(i, n)   for(int i = 0; i < (n); i++)
#define REPS(i, n)  for(int i = 1; i <= (n); i++)
#define RREP(i, n)  for(int i = (n)-1; i >= 0; i--)
#define RREPS(i, n) for(int i = (n); i > 0; i--)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define YES cout << "YES" << endl
#define Yes cout << "Yes" << endl
#define yes cout << "yes" << endl
#define NO cout << "NO" << endl
#define No cout << "No" << endl
#define no cout << "no" << endl

using ll  = long long;
using pi  = pair<int, int>;
using pl  = pair<ll, ll>;
using vi  = vector<int>;
using vl  = vector<ll>;
using vs  = vector<string>;
using vb  = vector<bool>;
using vvi = vector<vi>;
using vvl = vector<vl>;

//const int MOD = 1e9 + 7;
const int MOD = 998244353;
const int INF = 1e9 + 7;
const ll  INFL = 1e18;
const double PI = 3.141592653589793;
const double EPS = 1e-9;

template<class T> bool chmax(T &a, const T &b) { if(a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, const T &b) { if(a > b) { a = b; return true; } return false; }

signed main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);

    ll N; cin >> N;
    ll ans = 0;
    REP(i, N) 
    {
      ll A, B; cin >> A >> B;
      A--;
      ans += B*(B+1)/2;
      ans -= A*(A+1)/2;
    }
    cout << ans << endl;
}
#include <iostream>
using namespace std;

int main() {
	int N;
	cin >> N;
	long long A[N], B[N];
	long long sum = 0;
	for (int i = 0; i < N; i++) {
		cin >> A[i] >> B[i];
		sum = sum + 0.5 * (B[i] - A[i] + 1)*(A[i] + B[i]);
	}
	
	
	cout << sum << endl;
	return 0;
}