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.
import sys
import os.path
import functools
import itertools
import re

def solve():
    # code goes here!!         
    n = int(input())
    a = [0] * n
    p = [0] * n
    for i in range(n):
        a[i],p[i] = map(int,input().split())
    ans = 0
    i = 0
    cur = 0
    while i < n :
        cur = i
        while cur < n and p[i] <= p[cur] :
            ans += a[cur] * p[i]
            cur += 1
        i = cur
    print(ans)
        

def main():
    if os.path.exists('test.inp') :
        sys.stdin = open("test.inp","r")
    solve()

if __name__ == '__main__':
    main()


