// includes
#include <cstdio>
#include <cstdint>
#include <iostream>
#include <iomanip>
#include <string>
#include <queue>
#include <stack>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <utility>
#include <functional>
#include <cmath>
#include <climits>
#include <bitset>
#include <list>
#include <random>

// macros
#define ll long long int
#define pb emplace_back
#define mk make_pair
#define pq priority_queue
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())

using namespace std;

//  types
typedef pair<int, int> P;
typedef pair<ll, int> Pl;
typedef pair<ll, ll> Pll;
typedef pair<double, double> Pd;
 
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1e9 + 7;

// solve
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}

struct art{
  ll a, b;
  art(ll a, ll b): a(a), b(b){}
  art(): art(0, 0){}
};

ll dp[2001][2001];

int main(int argc, char const* argv[])
{
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  vector<ll> a(n), b(n);
  rep(i, n)cin >> a[i] >> b[i];
  vector<art> vec(n);
  rep(i, n)vec[i] = art(a[i], b[i]);
  int day = 0;
  int nt = 1;
  while(nt < n){
    day++;
    if(day % 2 == 1){
      nt += 2;
    }else{
      nt += 1;
    }
  }
  sort(all(vec), [](const art &x, const art &y){return x.b > y.b;});
  for(int i = 0; i <= n; i++){
    for(int j = 0; j <= day + 1; j++)dp[i][j] = linf;
  }
  dp[0][0] = 0;
  for(int i = 0; i < n; i++){
    for(int j = 0; j <= day+1; j++){
      dp[i+1][j] = dp[i][j];
      if(j > 0)dp[i+1][j] = min(dp[i+1][j], dp[i][j-1] + vec[i].a + vec[i].b * (j-1));
    }
  }
  cout << dp[n][day + 1] << endl;
	return 0;
}