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.
# coding: utf-8
n = int(input())
amounts = []
prices = []

for i in range(n):
  amount, price = input().split(" ")
  amounts.append(int(amount))
  prices.append(int(price))
  
def select_best_day(today):
  best_day = today
  c = today

  while c >= 0:
    if prices[c] < prices[best_day]:
      best_day = c
    c -= 1

  return best_day

solution = n * [0]
i = n - 1
while i >= 0:
  best_day = select_best_day(i)
  solution[best_day] += amounts[i]
  i -= 1

cost = 0
for index in range(n):
  cost += solution[index] * prices[index]

print(cost)