#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
typedef long long ll;
using namespace std;
const int maxn = 1e5 + 5;
int d[maxn], H = 0; // rozdiel oproti predoslemu, posledny aktivny stlpec
set<int> b;
void add(int l, int r) // chceme pridat l a r vratane
{
if (r < l) return;
d[l]++, d[r + 1]--;
if (d[l] == 0) b.erase(l);
if (d[r + 1] < 0) b.insert(r + 1);
}
struct mast { int h, k; } ship[maxn];
bool cmp(const mast& a, const mast& b) { return a.h < b.h; }
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
int n; cin >> n;
for (int i = 0; i < n; i++) cin >> ship[i].h >> ship[i].k;
sort(ship, ship + n, cmp);
b.insert(1);
//cout << "\n";
for (int i = 0; i < n; i++)
{
if (H != ship[i].h)
{
if (H && d[H + 1] == 0) b.erase(H + 1);
H = ship[i].h;
b.insert(H + 1);
}
int l = H - ship[i].k + 1;
int l1 = *b.lower_bound(l), r1 = H;
int len = ship[i].k - max(0, r1 - l1 + 1);
int l2 = *prev(b.upper_bound(l)), r2 = l2 + len - 1;
add(l1, r1);
add(l2, r2);
/*for (int i = 1, val = d[1]; i <= H; val += d[++i])
cout << val << " ";
cout << "\n";*/
}
ll ans = 0;
for (int i = 1, val = d[1]; i <= H; val += d[++i])
{
ans += val * 1ll * (val - 1) / 2ll;
}
cout << ans << "\n";
return 0;
}
