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.
n = int(input())
i = 0
data = list()
while i < n:
    num = input()
    arr = []
    counting = 0

    for m in range(0, len(num)):
        if num[m] == ' ':
            arr.append(int(num[counting:m]))
            counting = m + 1
        elif m == len(num) - 1:
            arr.append(int(num[counting:len(num)]))
    data.append(arr)
    i += 1

money = 0
check = None
for i in range(len(data)):
    if i == 0:
        money = data[i][0] * data[i][1]
        check = data[i][1]
    else:
        if check < data[i][1]:
            money += data[i][0] * check
        else:
            money += data[i][0] * data[i][1]
            check = data[i][1]
print(money)


