#include <bits/stdc++.h>

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)
#define unless(p) if(!(p))
#define until(p) while(!(p))

using ll = std::int64_t;
using P = std::tuple<ll,ll>;

int N, M;
P ps[2100];
ll dp[2100][2100];

ll rec(int i, int n, int m){
    if(i == N){
        return 0;
    }

    if(dp[i][n] != -1){
        return dp[i][n];
    }

    ll mn = std::numeric_limits<ll>::max();
    ll B, A;
    std::tie(B, A) = ps[i];

    if(n < N - M){
        mn = A + B * n + rec(i + 1, n + 1, m);
    }

    if(m < M){
        mn = std::min(mn, rec(i + 1, n, m + 1));
    }

    return dp[i][n] = mn;
}

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    std::cin >> N;

    M = N / 3;

    for(int i=0;i<N;++i){
        ll A, B;
        std::cin >> A >> B;

        ps[i] = std::make_tuple(B, A);
    }

    std::sort(ps, ps + N);
    std::reverse(ps, ps + N);

    memset(dp, -1, sizeof(dp));

    ll mn = rec(0, 0, 0);
    std::cout << mn << std::endl;
}