#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
int n; cin >> n;
vector<pair<int, int>> v(n);
for (int i = 0; i < n; i ++) cin >> v[i].first >> v[i].second;
sort(v.begin(), v.end());
vector<int> db(v[n - 1].first);
for (int i = 0; i < n; i ++) {
int ind = v[i].first - v[i].second;
int x = db[ind];
int a = ind, b = ind;
while (a >= 0 && db[a] == x) a --;
while (b < db.size() && db[b] == x) b ++;
a ++; b --;
int cnt = 0;
for (int j = b +1 ; j < v[i].first; j ++) {
db[j] ++; cnt ++;
}
for (int j = a; j < a + v[i].second - cnt; j ++) db[j] ++;
}
ll ans = 0;
for (int c : db) ans += c * (c - 1) / 2;
cout << ans;
return 0;
}
