#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <map>
#include <set>
#include <climits>
#include <cmath>
#include <fstream>
#include <queue>
#include <stack>
#include <bitset>
//#include "molecules.h"
using namespace std;
#define ll long long
//cin.tie(0);ios_base::sync_with_stdio(0);
const int MAXN = 1e5 + 5;
vector<int> cnt(MAXN);
/*struct segtree {
int size;
vector<ll> tree;
void init(int n) {
size = 1;
tree.assign(4 * n, 0LL);
size = n;
}
void build(vector<ll>& a, int x, int lx, int rx) {
if (rx == lx) {
if (lx < a.size()) {
tree[x] = lx;
}
return;
}
int m = (lx + rx) / 2;
build(a, 2 * x, lx, m);
build(a, 2 * x + 1, m + 1, rx);
//tree[x] = min(cnt[tree[2 * x]], cnt[tree[2 * x + 1]]);
if (cnt[tree[2 * x]] < cnt[tree[2 * x + 1]]) {
tree[x] = 2 * x;
}
else {
tree[x] = 2 * x + 1;
}
}
void build(vector<ll>& a) {
build(a, 1, 0, size - 1);
}
ll sum(int v, int tl, int tr, int l, int r) {
if (l > r) {
return 0;
}
if (l == tl && r == tr) {
return tree[v];
}
int tm = (tl + tr) / 2;
ll s1 = sum(v * 2, tl, tm, l, min(r, tm));
ll s2 = sum(v * 2 + 1, tm + 1, tr, max(l, tm + 1), r);
//return s1 + s2;
if (cnt[s1] < cnt[s2]) {
return s1;
}
return s2;
}
ll sum(int l, int r) {
return sum(1, 0, size - 1, l, r);
}
void update(int v, int tl, int tr, int pos, ll x) {
if (tl == tr) {
tree[v] = tl;
}
else {
int tm = (tl + tr) / 2;
if (pos <= tm) {
update(v * 2, tl, tm, pos, x);
}
else {
update(v * 2 + 1, tm + 1, tr, pos, x);
}
//tree[v] = tree[2 * v] + tree[2 * v + 1];
if (cnt[tree[2 * v]] < cnt[tree[2 * v + 1]]) {
tree[v] = tree[2 * v];
}
else {
tree[v] = tree[2 * v + 1];
}
}
}
void update(int idx, ll val) {
update(1, 0, size - 1, idx, val);
}
};*/
int main() {
int n;
cin >> n;
vector<pair<int, int>> p;
for (int i = 0; i < n; i++) {
int a, b;
cin >> a >> b;
p.push_back({ a, b });
}
sort(p.begin(), p.end());
ll ans = 0;
for (int i = 0; i < n; i++) {
vector<pair<int, int>> pq;
for (int j = 0; j < p[i].first; j++) {
pq.push_back({ cnt[j], j });
}
sort(pq.begin(), pq.end());
for (int j = 0; j < p[i].second; j++) {
ans += pq[j].first;
cnt[pq[j].second]++;
}
}
cout << ans << endl;
}
