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.
num = int(input())
a = []
b = []
for x in range(num):
    temp = input().split(" ")
    b.append(int(temp[0]))
    a.append(int(temp[1]))
    pass

cost = 0
lowestday = num
day = num

while len(a[:lowestday]) > 0:
    c = a[:lowestday]
    lowestprice = min(c)
    lowestday = a.index(min(c))
    #print("lowestprice", lowestprice)
    #print("lowestday", lowestday)
    if a[lowestday:]:
        cost += sum([lowestprice * x for x in b[lowestday:day]])
        # print(a[lowestday:])
        # print(cost)
        pass
    day = lowestday
    # print(a[:lowestday])
    pass

print(cost)
