#include <bits/stdc++.h>
#define ll long long
#define endl "\n"
using namespace std;
const int mxN = 100005;
struct STsum{
int len=1;
vector<int> tree;
STsum(int l){
while(len<l)
len*=2;
tree=vector<int>(2*len,0);
}
void update(int idx,int v){
idx += len;
tree[idx]+=v;
for(idx/=2;idx>=1;idx/=2)
tree[idx]=tree[idx*2]+tree[idx*2+1];
}
void range_update(int l,int r,int v){
update(l,v);
update(r+1,-v);
}
int query(int idx){
int l=1,r=idx;
int res = 0;
l+=len,r+=len;
while(l<=r){
if(l%2==1)
res += tree[l++];
if(r%2==0)
res += tree[r--];
l/=2,r/=2;
}
return res;
}
int lb(int v){
int idx = len;
int lo=1,hi=len-1;
while(lo<=hi){
int mid = lo+(hi-lo)/2;
if(query(mid)<=v){
idx=mid;
hi=mid-1;
}
else
lo=mid+1;
}
return idx;
}
};
void solve(){
int N;
cin >> N;
vector<pair<int,int>> event(N);//h,k
for(int i=0;i<N;i++){
cin >> event[i].first >> event[i].second;
}
sort(event.begin(),event.end());
STsum seg(mxN+5);
for(auto [h,k] : event){
int x = seg.query(h-k+1);
int l = seg.lb(x),r=min(seg.lb(x-1),h+1)-1;
int extra = max(0,k-(h-r));
if(extra>0){
seg.range_update(l,l+extra-1,1);
seg.range_update(r+1,h,1);
}
else{
seg.range_update(h-k+1,h,1);
}
}
ll ans = 0;
for(int i=1;i<mxN;i++){
int v = seg.query(i);
ans+=1LL*(v-1)*v/2;
}
cout << ans << endl;
}
int main(){
//ios::sync_with_stdio(false);
//cin.tie(0);
int t=1;
//cin >> t;
while(t--){
solve();
}
}
