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 solution():
    n = int(input())
    a, p = [], []
    res = 0
    for i in range(n):
        list1 = input().split()
        a.append(int(list1[0]))
        p.append(int(list1[1]))
    i = 0
    sum = 0
    price = 0
    for i in range(n):
        if p[i] < p[i - 1]:
            if i == n - 1:
                res += a[i] * p[i]
            res += a[i - 1] * p[i - 1]
            sum = a[i]
            price = p[i]
        else:
            sum += a[i]
            # print(sum)
            # print(price)
            res += sum * price
    print(res)


solution()

 				  	 	  		 	   		   		 	  	