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())
    duff = []
    cost = []
    for i in range(n):
        x = input().split()
        duff.append(int(x[0]))
        cost.append(int(x[1]))
    store = 0
    money = duff[0]*cost[0]
    i = 1
    while i <= n-1:
        
        if i < n-1:
            if cost[i] > cost[i+1]:
                money += duff[i] * cost[i]
                i += 1
            else:
                needed = duff[i]
                j = i+1
                min_cost = cost[i]
                while j <= n-1 and cost[i] < cost[j]:
                    needed += duff[j]
                    j += 1
                money += min_cost*needed
                i = j
        elif i == n-1:
            money += duff[i] * cost[i]
            i += 1
    print(money)
main()
            
            
            
            
        
    
