n = int(input())
l = [list(map(int, input().split())) for _ in range(n)]

x = 0
for i in l:
    if i[0] % 2 == 0:
        x += (i[0] // 2) * i[1]
    else:
        x += ((i[0]+1) // 2) * i[1]

x = x % (10**9+7)

print(x)