/*
author : PakinDioxide
created : 26/05/2025 19:47
task : IOI07_sails
*/
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int mxN = 1e5+5;
int n;
pair <ll, ll> a[mxN];
ll fen[mxN], idx = LLONG_MAX, ans = 0, t;
void upd(int idx, ll x) { for (int i = idx; i <= mxN; i += i & -i) fen[i] += x; }
ll qr(int idx) { ll x = 0; for (int i = idx; i > 0; i -= i & -i) x += fen[i]; return x; }
int main() {
ios::sync_with_stdio(0), cin.tie(0);
cin >> n;
for (int i = 1; i <= n; i++) cin >> a[i].first >> a[i].second;
sort(a+1, a+n+1), reverse(a+1, a+n+1);
for (int i = 1; i <= n; i++) {
auto &[h, c] = a[i];
idx = min(idx, h);
if (idx >= c) upd(idx+1, -1), upd(idx-c+1, 1), idx -= c, c = 0;
else upd(idx+1, -1), upd(1, 1), c -= idx, idx = 0;
if (idx == 0) idx = h;
upd(idx+1, -1), upd(idx-c+1, 1), idx -= c, c = 0;
if (idx == 0) idx = h;
}
for (int i = 1; i < mxN; i++) t = qr(i), ans += t*(t-1)/2;
cout << ans << '\n';
}
/*
if there are n sails on each hight, the inefficiency will be n*(n-1)/2
we sort the mast from long to short
*/
