#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 = 0) {
        if (_n <= 0) _n = 1;
        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[i];
                lz[2 * i + 1] += lz[i];
            }
            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] += val;
            lz[i] += val;
            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) {
        if (u > r || v < l) return inf;
        lazy(i, l, r);
        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 ql, int qr, int val) {
        if (ql > r || qr < l) return -1;
        lazy(i, l, r);
        if (st[i] > val) return -1;
        if (l == r) return l;
        int mid = (l + r) / 2;
        int ans = findL(2 * i, l, mid, ql, qr, val);
        if (ans != -1) return ans;
        return findL(2 * i + 1, mid + 1, r, ql, qr, val);
    }
};
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);
    int maxx = 0;
    for (int i = 1; i <= n; i++) maxx = max(maxx, a[i].fi);
    if (maxx <= 0) {
        cout << 0;
        return 0;
    }
    ST st(maxx);
    for (int i = 1; i <= n; i++) {
        int rbound = a[i].fi;
        if (rbound < 1) continue;
        int value = st.get(1, 1, maxx, 1, rbound);
        int L = st.findL(1, 1, maxx, 1, rbound, value);
        if (L == -1) continue;
        int R = min(a[i].fi, L + a[i].se - 1);
        if (L <= R) 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;
            int rightBound = L - remain;
            if (rightBound >= 1) {
                value = st.get(1, 1, maxx, 1, rightBound);
                int nxtL = st.findL(1, 1, maxx, 1, rightBound, value);
                if (nxtL != -1)
                    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:73:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |         freopen(".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~
sails.cpp:74:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   74 |         freopen(".out", "w", stdout);
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