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 sum(massive):
    fin = 0
    for i in range(len(massive)):
        fin += massive[i][0]*massive[0][1]
    return fin
 
def main():
    count = int(input())
    final = 0
 
    every = [0] * count
    price = [0] * count
 
    tmp = 0
 
    for i in range(count):
        tmp = list(map(int, input().split()))
        every[i] = tmp
        price[i] = tmp[1]
 
    price = list(set(price))
    price.sort()
 
    for a in range(len(price)):
        for i in range(count):
            try:
                if every[i][1] == price[a]:
                    final += sum(every[i:])
                    every = every[:i]
            except:
                break
    print(final)
 
if __name__ == '__main__':
    main()