#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
typedef long double ld;
const ll INF = mod * mod;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
int n;
LP x[2000];
ll dp[2001][2001];
int main() {
	cin >> n;
	rep(i, n) {
		cin >> x[i].second >> x[i].first;
	}
	sort(x, x + n,greater<LP>());
	
	rep(i, n+1) {
		rep(j, n + 1) {
			dp[i][j] = INF;
		}
	}
	dp[0][0] = 0;
	int m = n; int cop = n;
	while (cop > 0) {
		cop--;
		if (cop >= 2) {
			m--;
		}
		cop -= 2;
	}
	rep(i, n) {
		rep(j, i + 1) {
			//買う
			dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + x[i].second + j * x[i].first);
			//買わない
			dp[i + 1][j] = min(dp[i + 1][j], dp[i][j]);
		}
	}
	cout << dp[n][m] << endl;
	//stop
	return 0;
}