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 traceback
from contextlib import contextmanager
from io import StringIO


def min_cost(n, ap):
    m = ap[0][1]
    t = 0
    for a, p in ap:
        m = min(m, p)
        t += a*m
    return t


def pap():
    a, p = map(int, input().split())
    return a, p


def main():
    n = int(input())
    ap = [pap() for _ in range(n)]
    print(min_cost(n, ap))


def log(*args, **kwargs):
    print(*args, **kwargs, file=sys.stderr)


@contextmanager
def patchio(i):
    try:
        sys.stdin = StringIO(i)
        sys.stdout = StringIO()
        yield sys.stdout
    finally:
        sys.stdin = sys.__stdin__
        sys.stdout = sys.__stdout__


def do_test(k, test):
    try:
        log(f"TEST {k}")
        i, o = test
        with patchio(i) as r:
            main()
        b = float(o)
        try:
            a, = map(float, r.getvalue().splitlines())
        except Exception:
            ok = False
        else:
            ok = abs(a-b)/max(1,b) <= 0.0001
        if ok:
            log("OK\n")
        else:
            log(f"Expected:\n{o}Got:\n{r.getvalue()}")
    except Exception:
        traceback.print_exc()
        log()


def test(ts):
    for k in ts or range(len(tests)):
        do_test(k, tests[k])


tests = [("""\
3
1 3
2 2
3 1
""", """\
10
"""), ("""\
3
1 3
2 1
3 2
""", """\
8
""")]


if __name__ == '__main__':
    from argparse import ArgumentParser
    parser = ArgumentParser()
    parser.add_argument('--test', '-t', type=int, nargs='*')
    args = parser.parse_args()
    main() if args.test is None else test(args.test)

