MOD = 1000000007

def power(x,n) :
    if n==0 :
        return 1
    if n==1 :
        return x%MOD
    
    half = power(x,n//2)
    result = (half*half)%MOD
    
    if n%2==1 :
        result = (result*x)%MOD
    
    return result

inverse_element_MOD = lambda x: power(x, MOD-2)
expect_value = lambda a, b : (a*inverse_element_MOD(b))%MOD

result = 0
for _ in range(int(input())) :
    S, N = map(int, input().split())
    result = (result + expect_value(N,S))%MOD

print(result)