#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
const int N = 1e5 + 5;
int n, lz[N * 4];
struct node {
int val, mx;
node() : val(0), mx(0) {}
node(int val) : val(val), mx(val) {}
friend node operator + (const node &l, const node &r) {
node res = node();
res.val = l.val + r.val;
res.mx = max(l.mx, r.mx);
return res;
}
} segm[N * 4];
void push (int l, int r, int idx) {
segm[idx].val += (r - l + 1) * lz[idx];
segm[idx].mx += lz[idx];
if (l < r) {
lz[idx * 2 + 1] += lz[idx];
lz[idx * 2 + 2] += lz[idx];
}
lz[idx] = 0;
}
void upd (int l, int r, int idx, int tl, int tr, int val) {
push(l, r, idx);
if (l > tr || r < tl) return;
if (l >= tl && r <= tr) {
lz[idx] += val;
push(l, r, idx);
return;
}
int mid = (l + r) >> 1;
upd(l, mid, idx * 2 + 1, tl, tr, val);
upd(mid + 1, r, idx * 2 + 2, tl, tr, val);
segm[idx] = segm[idx * 2 + 1] + segm[idx * 2 + 2];
}
node qr (int l, int r, int idx, int tl, int tr) {
push(l, r, idx);
if (l > tr || r < tl) return node();
if (l >= tl && r <= tr) return segm[idx];
int mid = (l + r) >> 1;
return qr(l, mid, idx * 2 + 1, tl, tr) + qr(mid + 1, r, idx * 2 + 2, tl, tr);
}
int main() {
scanf("%d", &n);
vector<pii> c(n);
for (auto &[x, y]: c) scanf("%d %d", &x, &y);
reverse(c.begin(), c.end());
int k = 1e5;
for (auto &[x, y]: c) {
int cmn = 1, cmx = x;
int z0 = qr(1, k, 0, 1, 1).val, zn = qr(1, k, 0, x, x).val;
if (z0 < zn) {
{
int l = cmn, r = cmx;
while (l < r) {
int mid = (l + r + 1) >> 1;
if (qr(1, k, 0, cmn, mid).mx == z0) l = mid;
else r = mid - 1;
}
int z = min(y, l);
upd(1, k, 0, cmn, cmn + z - 1, 1);
y -= z;
cmn += z;
}
} else {
{
int l = cmn, r = cmx;
while (l < r) {
int mid = (l + r) >> 1;
if (qr(1, k, 0, mid, cmx).mx == zn) r = mid;
else l = mid + 1;
}
int z = min(y, cmx - l + 1);
upd(1, k, 0, cmx - z + 1, cmx, 1);
y -= z;
cmx -= z;
}
{
int l = cmn, r = cmx;
while (l < r) {
int mid = (l + r + 1) >> 1;
if (qr(1, k, 0, cmn, mid).mx == z0) l = mid;
else r = mid - 1;
}
int z = min(y, l);
upd(1, k, 0, cmn, cmn + z - 1, 1);
y -= z;
cmn += z;
}
}
upd(1, k, 0, cmx - y + 1, cmx, 1);
}
ll ans = 0;
for (int i = 1; i <= 10; i++) {
int z = qr(1, k, 0, i, i).val;
ans += z * (z - 1) / 2;
}
printf("%lld", ans);
}
