n = int(input())
c_list = []
d_list = []
for i in range(n):
    ci, di = [int(i) for i in input().split()]
    c_list.append(ci)
    d_list.append(di)
    
res = 0
for i in range(n):
    people_per_desk = 0
    
    if c_list[i] % 2 == 0:
        people_per_desk = int(c_list[i]//2)
    elif c_list[i] % 2 != 0:
        people_per_desk = int(c_list[i]//2 + 1)
        
    res += (people_per_desk * d_list[i]) % (10**9 + 7)
    
print(res)