#include <bits/stdc++.h>
using namespace std;
 
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef long double ld;

int n;
const int MAXN = 101;
ll big = 1000000007;
vl F,T,ind;

unordered_map<int,ll> DP;

bool comp(int i, int j){
    return T[i] < T[j];
}

ll dp(int i, int free){
    if(i < 0)return 0;
    int h = i * 1000 * 1000 + free;
    if(DP.find(h) != DP.end())return DP[h];
    ll ans = big*big;
    int j = ind[i];

    rep(new_free,0,F[j]+1){
        int rm = F[j]-new_free;
        if(rm <= free){
            ll temp = new_free * T[j] + dp(i-1, free-rm+new_free);
            ans = min(ans, temp);
        }
    }
    
    DP[h] = ans;
    return ans;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    
    cin >> n;
    rep(c1,0,n){
        int f,t;
        cin >> f >> t;
        F.push_back(f);
        T.push_back(t);
        ind.push_back(c1);
    }
    sort(all(ind), comp);
    cout << dp(n-1,0) << "\n";

    return 0;
}