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.
"""Solution & helper classes"""
class Solution:
    """__init__ & solve_and_print methods"""
    def __init__(self):
        self.__n = int(input())
        self.__a, self.__p = [], []
        for _ in range(self.__n):
            _a, _p = [int(x) for x in input().split()]
            self.__a.append(_a)
            self.__p.append(_p)

    def solve_and_print(self):
        """Solves the problem & prints the output"""
        min_price = float('inf')
        min_money = 0
        for _a, _p in zip(self.__a, self.__p):
            min_price = min(min_price, _p)
            min_money += (min_price* _a)
        print(min_money)

if __name__ == "__main__":
    Solution().solve_and_print()
