#include <bits/stdc++.h>
using namespace std;
vector<int> mini, maxi, lz;
int ss;
void lzy(int curin, int curl, int curr) {
if (curl == curr) {
maxi[curin] += lz[curin];
mini[curin] += lz[curin];
lz[curin] = 0;
return;
}
lz[curin * 2 + 1] += lz[curin];
lz[curin * 2 + 2] += lz[curin];
maxi[curin] += lz[curin];
mini[curin] += lz[curin];
lz[curin] = 0;
}
int ql, qr;
void upd(int curin, int curl, int curr) {
lzy(curin, curl, curr);
if (ql > curr || qr < curl)
return;
if (ql <= curl && curr <= qr) {
lz[curin] = 1;
return lzy(curin, curl, curr);
}
upd(curin * 2 + 1, curl, (curl + curr) / 2);
upd(curin * 2 + 2, (curl + curr) / 2 + 1, curr);
maxi[curin] = max(maxi[curin * 2 + 1], maxi[curin * 2 + 2]);
mini[curin] = min(mini[curin * 2 + 1], mini[curin * 2 + 2]);
}
int qval;
int lmost(int curin, int curl, int curr) {
lzy(curin, curl, curr);
if (curl == curr)
return curl;
lzy(curin * 2 + 1, curl, (curl + curr) / 2);
lzy(curin * 2 + 2, (curl + curr) / 2 + 1, curr);
if (mini[curin * 2 + 1] <= qval && qval <= maxi[curin * 2 + 1]) {
return lmost(curin * 2 + 1, curl, (curl + curr) / 2);
}
assert(mini[curin * 2 + 2] <= qval && qval <= maxi[curin * 2 + 2]);
return lmost(curin * 2 + 2, (curl + curr) / 2 + 1, curr);
}
int rmost(int curin, int curl, int curr) {
lzy(curin, curl, curr);
if (curl == curr)
return curl;
lzy(curin * 2 + 1, curl, (curl + curr) / 2);
lzy(curin * 2 + 2, (curl + curr) / 2 + 1, curr);
if (mini[curin * 2 + 2] <= qval && qval <= maxi[curin * 2 + 2])
return rmost(curin * 2 + 2, (curl + curr) / 2 + 1, curr);
return rmost(curin * 2 + 1, curl, (curl + curr) / 2);
}
int qin;
int qry(int curin, int curl, int curr) {
lzy(curin, curl, curr);
if (curl == curr) {
return maxi[curin];
}
int mid = (curl + curr) / 2;
if (qin <= mid)
return qry(curin * 2 + 1, curl, mid);
return qry(curin * 2 + 2, mid + 1, curr);
}
int main() {
int n;
cin >> n;
vector<pair<int, int>> vpii(n);
for (auto& [a, b] : vpii)
cin >> a >> b;
sort(vpii.begin(), vpii.end());
ss = vpii.back().first;
mini = maxi = lz = vector<int>(4 * ss);
for (auto [height, amt] : vpii) {
int l = height - amt;
qin = l;
int val = qry(0, 0, ss - 1);
qval = val;
int ll = lmost(0, 0, ss - 1), rr = min(height - 1, rmost(0, 0, ss - 1));
if (rr == height - 1) {
ql = ll, qr = ll + amt - 1;
upd(0, 0, ss - 1);
}
else {
ql = rr + 1, qr = height - 1;
upd(0, 0, ss - 1);
int k = amt - (qr - ql + 1);
ql = ll, qr = ql + k - 1;
upd(0, 0, ss - 1);
}
}
long long ans = 0;
for (int i = 0; i < ss; i++) {
qin = i;
long long smth = qry(0, 0, ss - 1);
ans += smth * (smth - 1) / 2;
}
cout << ans << "\n";
}
