#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MAXN = 1e5 + 10;
struct node{
ll max, lz;
};
int k[MAXN];
node seg[4 * MAXN];
void refresh(int x, int lx, int rx){
if(lx != rx){
int lc = 2 * x, rc = 2 * x + 1;
seg[lc].lz += seg[x].lz;
seg[rc].lz += seg[x].lz;
}
seg[x].max += seg[x].lz;
seg[x].lz = 0;
}
void update(int x, int lx, int rx, int l, int r){
refresh(x, lx, rx);
if(rx < l || lx > r) return;
if(l <= lx && rx <= r){
seg[x].lz ++;
refresh(x, lx, rx);
return;
}
int m = (lx + rx) / 2, lc = 2 * x, rc = 2 * x + 1;
update(lc, lx, m, l, r);
update(rc, m + 1, rx, l, r);
seg[x].max = max(seg[lc].max, seg[rc].max);
}
int bs(int x, int lx, int rx, int l, int r, int val){
refresh(x, lx, rx);
if(rx < l || lx > r || seg[x].max <= val) return -1;
if(lx == rx) return lx;
int m = (lx + rx) / 2, lc = 2 * x, rc = 2 * x + 1;
int bs_r = bs(rc, m + 1, rx, l, r, val);
if(bs_r != -1) return bs_r;
return bs(lc, lx, m, l, r, val);
}
ll query(int x, int lx, int rx, int i){
refresh(x, lx, rx);
if(lx == rx) return seg[x].max;
int m = (lx + rx) / 2, lc = 2 * x, rc = 2 * x + 1;
if(i <= m) return query(lc, lx, m, i);
return query(rc, m + 1, rx, i);
}
int main(){
cin.tie(0)->sync_with_stdio(0);
int n; cin >> n;
vector<pair<int, int>> masts;
int H = 0;
for(int i=1; i<=n; i++){
int h; cin >> h >> k[i];
masts.push_back({h, i});
H = max(H, h);
}
sort(masts.begin(), masts.end());
for(auto [h, i] : masts){
int j = h - k[i] + 1;
int v_j = query(1, 1, H, j);
int l_1 = bs(1, 1, H, 1, h, v_j) + 1;
l_1 = max(l_1, 1);
int l_2 = bs(1, 1, H, 1, h, v_j - 1) + 1;
if(l_2 <= h) update(1, 1, H, l_2, h);
update(1, 1, H, l_1, l_1 + (k[i] - (h - l_2 + 1)) - 1);
}
ll ans = 0;
for(int i=1; i<=H; i++){
ll q = query(1, 1, H, i);
ans += (q * (q - 1)) / 2;
}
cout << ans << "\n";
return 0;
}
