M = 10**9 + 7


def main(n, m):
    def f():
        return map(int, input().split())

    res = 0
    for _ in range(n):
        c, d = f()
        x = (c % m + 1) // 2
        x *= d % m
        res += x
    return res


print(main(int(input()), M))