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 mini(first, last, arr):
    minix = float('inf')
    for i in range(first, last):
        if minix > arr[i]:
            minix = arr[i]
    return minix

def solve():
    n = int(input())
    price = 0
    amount = []
    pricex = []
    for i in range(n):
        a, p = map(int, input().split())
        amount.append(a)
        pricex.append(p)
    minimum = pricex[0]
    index = []
    ind = 0
    for i in range(1, len(pricex)):
        if minimum > pricex[i]:
            minimum = pricex[i]
            index.append(i)
            ind = i
    i = 0
    # print(index[i])
    while i < len(index) - 1:
        for j in range(index[i], index[i + 1]):
            minimum = mini(index[i], index[i + 1], pricex)
            price += amount[j] * minimum
        i += 1
    minimum = pricex[ind]
    for i in range(ind, len(pricex)):
        price += amount[i] * minimum

    print(price)

solve()
