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.
daysNum = int(input())
requiredMeat = []
meatCost = []

for i in range(daysNum):
  inputs = input().split(" ")
  requiredMeat.append(int(inputs[0]))
  meatCost.append(int(inputs[1]))

spentMoney = 0
meatStock = 0

for i in range(daysNum):
  todayNeed = requiredMeat[i]
  todayCost = meatCost[i]
  
  if(meatStock == 0):
    for j in range(i + 1, daysNum):
      futureDayCost = meatCost[j]
      if(futureDayCost < todayCost):          
        break
      if (j == daysNum - 1):
        j += 1
        break
    meatQuant = 0
    if(i == daysNum - 1):
      j += 1
    for k in range(i, j):
      meatQuant += requiredMeat[k]
    spentMoney += meatQuant * todayCost
    meatStock = meatQuant

  #consume
  meatStock = meatStock - todayNeed
    
print(spentMoney)