#include <bits/stdc++.h>
using namespace std;
struct Node {
int val, lazy;
Node(int v) : val(v), lazy(0) {}
Node() : Node(0) {}
Node operator+(const Node &n) {
return Node(min(this->val, n.val));
}
};
#define MAXN 100100
pair<int, int> arr[MAXN];
Node seg[4*MAXN];
void build(int n, int l, int r) {
if(l==r) seg[n]=Node();
else {
int mid=(l+r)/2;
build(2*n, l, mid);
build(2*n+1, mid+1, r);
seg[n]=seg[2*n]+seg[2*n+1];
}
}
void lazyPropagation(int n, int l, int r) {
seg[n].val+=seg[n].lazy;
if(l<r) {
seg[2*n].lazy+=seg[n].lazy;
seg[2*n+1].lazy+=seg[n].lazy;
}
seg[n].lazy=0;
}
void update(int n, int l, int r, int p, int q, int v) {
if(l>q||p>r) {
lazyPropagation(n, l, r);
return;
}
if(l>=p&&r<=q) {
seg[n].lazy+=v;
lazyPropagation(n, l, r);
return;
}
int mid=(l+r)/2;
lazyPropagation(n, l, r);
update(2*n, l, mid, p, q, v);
update(2*n+1, mid+1, r, p, q, v);
seg[n]=seg[2*n]+seg[2*n+1];
}
int query(int n, int l, int r, int i) {
lazyPropagation(n, l, r);
if(l==r) return seg[n].val;
int mid=(l+r)/2;
if(i<=mid) return query(2*n, l, mid, i);
return query(2*n+1, mid+1, r, i);
}
int fstidx(int n, int l, int r, int v) {
lazyPropagation(n, l, r);
if(seg[n].val>v) return r+1;
if(l==r) return l;
int mid=(l+r)/2;
int lq=fstidx(2*n, l, mid, v);
if(lq<=mid) return lq;
return fstidx(2*n+1, mid+1, r, v);
}
#define MAXV 100000
int main() {
cin.tie(nullptr);
ios::sync_with_stdio(false);
int n;
cin >> n;
for(int i=0;i<n;i++) cin >> arr[i].first >> arr[i].second;
sort(arr, arr+n);
build(1, 1, MAXV);
for(int i=0;i<n;i++) {
int h=arr[i].first, k=arr[i].second;
int mn=h-k+1;
int val=query(1, 1, MAXV, mn);
int i1=fstidx(1, 1, MAXV, val);
int i2=fstidx(1, 1, MAXV, val-1);
if(i2<=h) update(1, 1, MAXV, i2, h, 1);
int cnt=min(i2, h+1)-mn;
update(1, 1, MAXV, i1, i1+cnt-1, 1);
}
int64_t ans=0;
for(int i=1;i<=MAXV;i++) {
int64_t cur=query(1, 1, MAXV, i);
ans+=cur*(cur-1)/2;
}
cout << ans << endl;
return 0;
}
