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.

n = int(input())

ap = []

for i in range(n) :
    
    ap.append(list(map(int,input().split())))
    
#done = {i:0 for i in range(n)}
cost = ap[0][0]*ap[0][1]   
for i in range(1,n) :
    #print(i)
    minn = ap[i][1] 
    
    for j in range(i-1,-1,-1) :
        
        #print(minn,ap[j][1])   
        if ap[j][1]<=minn :
            
            minn = ap[j][1]
            
    cost = cost + ap[i][0]*minn 
    #print(cost)
    
print(cost)
    
            
            
            
            
            
            
            
            
            
            
            