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.
from sys import stdin, stdout
 
def main():
 
    # input via readline method
    n = int(stdin.readline())
    

    a = []
    p = []
    arr = []
    for i in range(n):
        arr.append([int(x) for x in stdin.readline().split(" ")])
        a.append(arr[0][0])
        p.append(arr[0][1])
        arr = []

    cost = 0
    min_day = p.index(min(p))
    a_new = a[0:min_day]
    p_new = p[0:min_day]
    cost = cost + sum(a[min_day:])*p[min_day]
    while min_day != 0:
        #print("#",min_day)
        min_day = p_new.index(min(p_new))
        cost = cost + sum(a_new[min_day:])*p_new[min_day]
        a_new = a_new[0:min_day]
        p_new = p_new[0:min_day]
        
    print(cost)


    
    

 
            
       
 

# call the main method
if __name__ == "__main__":
    main()   