def main():
    N = int(input())
    CD = tuple(tuple(map(int, input().split())) for _ in [0] * N)

    n = 0
    m = 1000000007
    for c, d in CD:
        c = c % m
        d = d % m
        n += (c + 1) // 2 * d
        n = n % m
    print(n)

main()