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.
DAYS = []
N = -1
MAX_PRICE = 100

def entrypoint():
    global DAYS, N
    N = int(input())
    get_input = lambda : list(map(int, input().split()))
    
    def process_input():
        amount, price = get_input()
        DAYS.append({ 'amount': amount, 'price': price })

    [process_input() for _ in range(N)]

def process():
    curr_minimal = MAX_PRICE + 1
    
    for i in range(N):
        curr_minimal = min(curr_minimal, DAYS[i]['price'])
        DAYS[i]['price'] = curr_minimal

    compute_price_day = lambda x : x['amount'] * x['price']

    min_money = sum(list(map(compute_price_day, DAYS)))

    return min_money
def main():
    entrypoint()
    print(process())


if __name__ == '__main__':
    main()