#include <bits/stdc++.h>
/*
    Wake up, I'm wake up
    Thu sang roi, em thay khong?
*/
using namespace std;
using ll = long long;
#define int long long
#define pii pair<ll, ll>
#define fi first
#define se second
const ll N = 2e5 + 5, inf = 1e18, mod = 1e9 + 7, block = 320, lim = 19;
int n;
pii a[N];
struct ST {
    vector <int> st, lz;
    ST (int _n) {
        st.assign(4 * (_n + 1), 0);
        lz.assign(4 * (_n + 1), 0);
    }
    void lazy(int i, int l, int r) {
        if (lz[i] != 0) {
            if (l < r) {
                st[2 * i] += lz[i];
                st[2 * i + 1] += lz[i];
                lz[2 * i]++;
                lz[2 * i + 1]++;
            }
            lz[i] = 0;
        }
    }
    void update(int i, int l, int r, int u, int v, int val) {
        if (u > r || v < l) return;
        if (u <= l && r <= v) {
            st[i]++;
            lz[i]++;
            return;
        }
        lazy(i, l, r);
        int mid = (l + r) / 2;
        update(2 * i, l, mid, u, v, val);
        update(2 * i + 1, mid + 1, r, u, v, val);
        st[i] = min(st[2 * i], st[2 * i + 1]);
    }
    int get(int i, int l, int r, int u, int v) {
        lazy(i, l, r);
        if (u > r || v < l) return inf;
        if (u <= l && r <= v) return st[i];
        int mid = (l + r) / 2;
        return min(get(2 * i, l, mid, u, v), get(2 * i + 1, mid + 1, r, u, v));
    }
    int findL(int i, int l, int r, int val) {
        lazy(i, l, r);
        if (st[i] > val) return -1;
        if (l == r) return l;
        int mid = (l + r) / 2;
        int ans = -1;
        if (st[2 * i] <= val) ans = findL(2 * i, l, mid, val);
        if (ans == -1) ans = findL(2 * i + 1, mid + 1, r, val);
        return ans;
    }
} st(N);
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    if (fopen(".inp", "r")) {
        freopen(".inp", "r", stdin);
        freopen(".out", "w", stdout);
    }
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i].fi >> a[i].se;
    sort(a + 1, a + n + 1);
    // for (int i = 1; i <= n; i++) cout << a[i].fi << ' ' << a[i].se << '\n';
    int maxx = 0;
    for (int i = 1; i <= n; i++) maxx = max(maxx, a[i].fi);
    for (int i = 1; i <= n; i++) {
        // cout << a[i].fi << ' ' << a[i].se << '\n';
        int value = st.get(1, 1, maxx, 1, a[i].fi);
        // cout << value << '\n';
        int L = st.findL(1, 1, maxx, value);
        int R = min(a[i].fi, L + a[i].se - 1);
        st.update(1, 1, maxx, L, R, 1);
        if (L + a[i].se - 1 > a[i].fi) {
            int remain = (L + a[i].se - 1) - a[i].fi;
            value = st.get(1, 1, maxx, 1, L - remain);
            int nxtL = st.findL(1, 1, maxx, value);
            st.update(1, 1, maxx, nxtL, nxtL + remain - 1, 1);
        }
    }
    int ans = 0;
    for (int i = 1; i <= maxx; i++) {
        int val = st.get(1, 1, maxx, i, i);
        ans += val * (val - 1) / 2;
    }
    cout << ans;
    return 0;
}
Compilation message (stderr)
sails.cpp: In function 'int main()':
sails.cpp:72:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   72 |         freopen(".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~
sails.cpp:73:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |         freopen(".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... | 
| # | Verdict  | Execution time | Memory | Grader output | 
|---|
| Fetching results... |