Duff is addicted to meat! Malek wants to keep her happy for *n* days. In order to be happy in *i*-th day, she needs to eat exactly *a*<sub class="lower-index">*i*</sub> kilograms of meat.

There is a big shop uptown and Malek wants to buy meat for her from there. In *i*-th day, they sell meat for *p*<sub class="lower-index">*i*</sub> dollars per kilogram. Malek knows all numbers *a*<sub class="lower-index">1</sub>, ..., *a*<sub class="lower-index">*n*</sub> and *p*<sub class="lower-index">1</sub>, ..., *p*<sub class="lower-index">*n*</sub>. In each day, he can buy arbitrary amount of meat, also he can keep some meat he has for the future.

Malek is a little tired from cooking meat, so he asked for your help. Help him to minimize the total money he spends to keep Duff happy for *n* days.
The first line of input contains integer *n* (1 ≤ *n* ≤ 10<sup class="upper-index">5</sup>), the number of days.

In the next *n* lines, *i*-th line contains two integers *a*<sub class="lower-index">*i*</sub> and *p*<sub class="lower-index">*i*</sub> (1 ≤ *a*<sub class="lower-index">*i*</sub>, *p*<sub class="lower-index">*i*</sub> ≤ 100), the amount of meat Duff needs and the cost of meat in that day.
import sys
from os import path
if (path.exists('input.txt') and path.exists('output.txt')):
    sys.stdout = open('output.txt', 'w')
    sys.stdin = open('input.txt', 'r')


def main():
    N = int(input())
    needs = []
    costs = []
    for ii in range(N):
        a, p = map(int, input().split())
        needs.append(a)
        costs.append(p)
    
    ans = 0
    i = 0
    while i < N:
        curr_cost = costs[i]
        ans += needs[i] * curr_cost
        # print(i)
        for j in range(i + 1, N):
            if curr_cost < costs[j]:
                ans += needs[j] * curr_cost
                i += 1
            else:
                break
        i += 1
    
    print(ans)

main()