#include<bits/stdc++.h>
using namespace std;
using i64 = long long;
#define int i64
#define vi vector<int>
#define vvi vector<vi>
#define vb vector<bool>
#define pii pair<int, int>
#define fi first
#define se second
#define sz(x) (int)(x).size()
struct BIT{
vi bit;
BIT(int n) : bit(n + 2) {}
void add(int idx, int val){
for(++idx; idx < sz(bit); idx += idx & -idx)
bit[idx] += val;
}
int sum(int idx){
int ret = 0;
for(++idx; idx; idx -= idx & -idx)
ret += bit[idx];
return ret;
}
};
signed main(){
ios_base::sync_with_stdio(false); cin.tie(0);
int n, h, k, ans = 0, maxh = 0;
cin >> n;
vector<pii> mast(n);
vi cur_h;
for(int i = 0; i < n; i++){
cin >> mast[i].fi >> mast[i].se;
maxh = max(maxh, mast[i].fi);
}
sort(mast.begin(), mast.end());
BIT bit(maxh + 1);
auto find_smallest_index = [&](int lo, int hi, int val) -> int {
int ret = hi + 1;
while(hi >= lo){
int mid = lo + (hi - lo) / 2, cur = bit.sum(mid);
if(cur == val){
ret = mid;
hi = mid - 1;
}
else if(cur < val)
hi = mid - 1;
else
lo = mid + 1;
}
return ret;
};
auto find_greatest_index = [&](int lo, int hi, int val) -> int {
int ret = hi + 1;
while(hi >= lo){
int mid = lo + (hi - lo) / 2, cur = bit.sum(mid);
if(cur == val){
ret = mid;
lo = mid + 1;
}
else if(cur < val)
hi = mid - 1;
else
lo = mid + 1;
}
return ret;
};
auto range_add = [&](int l, int r, int val) -> void {
bit.add(l, val);
bit.add(r + 1, -val);
};
for(int i = 0; i < n; i++){
h = mast[i].fi, k = mast[i].se;
while(h > sz(cur_h))
cur_h.emplace_back(0);
int last_val = bit.sum(sz(cur_h) - k);
int l = find_smallest_index(0, sz(cur_h) - 1, last_val);
int r = find_greatest_index(0, sz(cur_h) - 1, last_val);
if(r + 1 < sz(cur_h)){
range_add(r + 1, sz(cur_h) - 1, 1);
int ln = (sz(cur_h) - 1) - (r + 1) + 1, rem = k - ln;
range_add(l, l + rem - 1, 1);
}
else{
range_add(l, l + k - 1, 1);
}
}
for(int i = 0; i < maxh; i++){
int val = bit.sum(i);
ans += val * (val - 1) / 2;
}
cout << ans;
return 0;
}
