#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("avx,avx2,fma")
#define int long long
#define F first
#define S second
#define pb push_back
#define endl '\n'
#define all(v) v.begin(),v.end()
#define gcd(a,b) __gcd(a,b)
#define mt make_tuple
#define pqueue priority_queue
typedef pair<int,int> ii;
typedef tuple<int,int,int> iii;
typedef tuple<int,int,int,int> iiii;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<string> vs;
typedef vector<char> vc;
typedef vector<iii> viii;
typedef set<int> si;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef vector<si> vsi;
typedef vector<vb> vvb;
typedef vector<vc> vvc;
const int MOD = 998244353;
const int N = 1e6 + 100;
int n;
vii mast;
int32_t main(){
ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
cin >> n;
mast.assign(n,{});
for (int i = 0; i < n; i++) cin >> mast[i].F >> mast[i].S;
sort(all(mast));
pqueue<int,vi,greater<int>> pq;
int old = 0,ans = 0;
for (int i = 0; i < n; i++){
while (old < mast[i].F){
pq.push(0);
old++;
}
vi tmp;
for (int i = 0; i < mast[i].S; i++){
tmp.pb(pq.top());
pq.pop();
}
for (int i = 0; i < mast[i].S; i++) pq.push(tmp[i] + 1);
}
while (!pq.empty()) {
ans += pq.top() * (pq.top() - 1) / 2;
pq.pop();
}
cout << ans << endl;
return 0;
}
