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 main():
    n = int(input())
    a = [0 for _ in range(n)]
    p = [0 for _ in range(n)]

    for i in range(n):
        [ai, pi] = [int(_) for _ in input().split()]
        a[i] = ai
        p[i] = pi

    sum_money = 0
    bought = [False for _ in range(n)]

    for i in range(n):
        if not bought[i]:
            try:
                j = next(index for index in range(i + 1, n) if p[index] < p[i])
            except StopIteration:
                j = n

            for k in range(i, j):
                sum_money += p[i] * a[k]
                bought[k] = True

    print(sum_money)


if __name__ == '__main__':
    main()
