#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

#include <atcoder/all>
using namespace atcoder;

#define REP(i, n) for(int i = 0; i < (int)n; i++)
#define LREP(i, n) for(LL i = 0; i < (LL)n; i++)
#define RREP(i, n) for(int i = (int)n-1; i >= 0; i--)
#define V(T) vector<T>

#define P pair<int, int>
#define LP pair<LL, LL>
#define T3 tuple<LL, LL, LL>
#define T4 tuple<LL, LL, LL, LL>
#define INF 1000000007
#define SIZE 500100
#define MOD 1000000007
typedef long long LL;

#define SIZE2 2010

LL N, M;
LL A[SIZE], B[SIZE];

bool done[SIZE2][SIZE2];
LL memo[SIZE2][SIZE2];
LL dfs(LL i, LL j) {
	if (i == N) {
		if (j == M) return 0;
		return 1e18;
	}
	if (done[i][j]) return memo[i][j];
	LL res = dfs(i + 1, j) + (A[i] + B[i] * (i - j));
	if (j < M) res = min(res, dfs(i + 1, j + 1));
	
	done[i][j] = true;
	return memo[i][j] = res;
}

int main() {
	cin >> N;
	REP(i, N) cin >> A[i] >> B[i];

	M = N / 3;
	V(LP) X;
	REP(i, N) X.push_back(LP(B[i], A[i]));
	sort(X.begin(), X.end(), greater<LP>());
	REP(i, N) {
		A[i] = X[i].second;
		B[i] = X[i].first;
	}

	cout << dfs(0, 0) << endl;
}