#include <bits/stdc++.h>
using namespace std;
//#define int long long
#define all(x) x.begin(), x.end()
int st[1 << 18] = {}, lz[1 << 18] = {}, st2[1 << 18] = {};
void down(int id)
{
if (!lz[id]) return;
lz[id << 1] += lz[id];
lz[id << 1 | 1] += lz[id];
st[id << 1] += lz[id];
st[id << 1 | 1] += lz[id];
st2[id << 1] += lz[id];
st2[id << 1 | 1] += lz[id];
lz[id] = 0;
}
void add_range(int u, int v, int val, int id = 1, int l = 1, int r = 1 << 17)
{
if (l > r) return;
if (r < u || l > v) return;
if (l >= u && r <= v)
{
st[id] += val;
st2[id] += val;
lz[id] += val;
return;
}
down(id);
int mid = (l + r) >> 1;
add_range(u, v, val, id << 1, l, mid);
add_range(u, v, val, id << 1 | 1, mid + 1, r);
st[id] = max(st[id << 1], st[id << 1 | 1]);
st2[id] = min(st2[id << 1], st2[id << 1 | 1]);
}
int get(int pos, int id = 1, int l = 1, int r = 1 << 17)
{
if (l == r) return st[id];
down(id);
int mid = (l + r) >> 1;
if (pos <= mid) return get(pos, id << 1, l, mid);
return get(pos, id << 1 | 1, mid + 1, r);
}
int find_left(int val, int id = 1, int l = 1, int r = 1 << 17)
{
if (l == r) return l;
down(id);
int mid = (l + r) >> 1;
if (st2[id << 1] <= val) return find_left(val, id << 1, l, mid);
return find_left(val, id << 1 | 1, mid + 1, r);
}
void find_right(int val, int h, int& ans, int id = 1, int l = 1, int r = 1 << 17)
{
if (ans != -1) return;
if (l > h) return;
if (l == r)
{
ans = l;
return;
}
down(id);
int mid = (l + r) >> 1;
if (st[id << 1 | 1] >= val) find_right(val, h, ans, id << 1 | 1, mid + 1, r);
if (st[id << 1] >= val) find_right(val, h, ans, id << 1, l, mid);
}
int32_t main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n;
vector<pair<int, int>> a;
for (int i = 0; i < n; i++)
{
int h, k;
cin >> h >> k;
a.emplace_back(h, k);
}
sort(all(a));
for (auto x : a)
{
int h = x.first, k = x.second;
if (h == k) add_range(1, h, 1);//, cout << "FULL\n";
else
{
if (get(h - k) != get(h - k + 1))
{
//cout << "ENOUGH\n";
add_range(h - k + 1, h, 1);
}
else
{
int val = get(h - k + 1);
int l = find_left(val);
int r = -1;
find_right(val, h, r);
add_range(r + 1, h, 1);
k -= h - r;
add_range(l, l + k - 1, 1);
//cout << l << ' ' << r << '\n';
}
}
//for (int i = 1; i <= 5; i++) cout << get(i) << ' ';
//cout << '\n';
}
long long ans = 0;
for (int i = 1; i <= 100000; i++)
{
long long s = get(i);
ans += s * (s - 1) / 2;
}
cout << ans;
return 0;
}
