#include <bits/stdc++.h>
using namespace std;
void just_do_it();
int main() {
#ifdef KAMIRULEZ
freopen("kamirulez.inp", "r", stdin);
freopen("kamirulez.out", "w", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(0);
just_do_it();
return 0;
}
const int maxn = 1e5 + 20;
pair<int, int> a[maxn];
int cnt[maxn];
int h;
int get(int pos) {
return cnt[pos];
}
void update(int lt, int rt) {
for (int i = lt; i <= rt; i++) {
cnt[i]++;
}
}
int find_max(int lt, int rt, int val) {
int res = -1;
while (lt <= rt) {
int mt = (lt + rt) / 2;
if (get(mt) >= val) {
res = mt;
lt = mt + 1;
}
else {
rt = mt - 1;
}
}
return res;
}
int find_min(int lt, int rt, int val) {
int res = -1;
while (lt <= rt) {
int mt = (lt + rt) / 2;
if (get(mt) <= val) {
res = mt;
rt = mt - 1;
}
else {
lt = mt + 1;
}
}
return res;
}
void just_do_it() {
int n;
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i].first >> a[i].second;
}
sort(a + 1, a + n + 1);
h = a[n].first;
for (int i = 1; i <= n; i++) {
int rt2 = a[i].first;
int rem = a[i].second;
int mt = rt2 - rem + 1;
int val = get(mt);
int rt1 = find_max(mt, h, val);
int lt = find_min(1, mt, val);
if (rt1 < rt2) {
update(rt1 + 1, rt2);
rem -= rt2 - rt1;
}
if (rem > 0) {
update(lt, lt + rem - 1);
}
}
long long res = 0;
for (int i = 1; i <= h; i++) {
res += 1LL * cnt[i] * (cnt[i] - 1) / 2;
}
cout << res;
}
