import sys
readline = sys.stdin.readline

ans = 1
mod = 10 ** 9 + 7
L = int(readline())
for i in range(L):
    d, e = map(int, readline().split())
    ans *= pow(d - 1, mod - 2, mod) * (d * (pow(d, e + 1, mod) - 1) * pow(d - 1, mod - 2, mod) - (e + 1)  )
    ans %= mod
print(ans)