#include <bits/stdc++.h>
#define el '\n'
#define FNAME "NAME"
#define allof(x) x.begin(),x.end()
#define allof1(x) x.begin()+1,x.end()
#define mset(x,n) memset(x,(n),sizeof(x))
using namespace std;
const long long MOD = (long long) 1e9 + 7;
template<class X,class Y> bool minimize(X &a,Y b){ if (a>b) {a=b; return true;} return false;}
template<class X,class Y> bool maximize(X &a,Y b){ if (a<b) {a=b; return true;} return false;}
void setup(){
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
if (fopen(FNAME".inp","r")){
freopen(FNAME".inp","r",stdin);
freopen(FNAME".out","w",stdout);
}
}
template<typename T>
struct FenwickTree{
int n;
vector<T> bit;
FenwickTree(int N=0){
n=N;
if (n>0){
bit.resize(n+1,0);
}
}
void update(int node,T val){
while (node<=n){
bit[node]+=val;
node += (node & -node);
}
}
T getVal(int node){
T res=0;
while (node>0){
res+=bit[node];
node -= (node & -node);
}
return res;
}
// Into difference BIT
inline void range(int l,int r,T val){
update(l,+val);
if (r+1<=n) update(r+1,-val);
}
inline T getRange(int l,int r){
return getVal(r) - getVal(l-1);
}
};
int n;
vector<pair<int,int>> a;
int MAXH;
void init(){
cin>>n;
a.resize(n);
for (auto &x : a) cin>>x.first>>x.second, maximize(MAXH, x.first);
sort(allof(a));
MAXH++;
}
inline long long nC2(long long x){
return x * (x - 1) / 2ll;
}
void sol(){
FenwickTree<int> bit(MAXH);
auto getThres = [&] (int x,int h) -> int {
int l = 1, r = h;
int res = 0;
while (l <= r){
int mid = (l + r) >> 1;
if (bit.getVal(mid) >= x){
res = mid;
l = mid + 1;
} else r = mid - 1;
}
return res;
};
// * take last k sails to avoid congestion
for (const auto &[h, k] : a){
int v = bit.getVal(h - k + 1);
int R = getThres(v, h);
int L = getThres(v + 1, h);
bit.range(R + 1, h, 1);
int leftover = h - R;
bit.range(L + 1, L + (k - h + R), 1);
}
long long res = 0;
for (int i = 0; i < MAXH; i++){
res += nC2(bit.getVal(i));
}
cout<<res;
}
int main(){
setup();
init();
sol();
}
