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.
def maximunMeat(values, days):
  amount = 0
  nDays = len(days)
  for i in range(nDays):
    day = days[i]
    cost = values[day]
    if cost != -1:
      amount += (cost * day)
      for j in range(i+1, nDays):
        dayJ = days[j]
        if values[dayJ] > cost:
          amount += (cost * dayJ)
          values[dayJ] = -1
        else:
          break

  return amount


days = int(input())
values = {}
daysList = []

for _ in range(days):
  day, cost = [int(x) for x in input().split(" ")]
  values[day] = cost
  daysList.append(day)

maxAmount = maximunMeat(values, daysList)
print(maxAmount)