def power(num, t): if t == 1: return num % d elif t % 2: return num * power(num, t - 1) % d else: p = power(num, t // 2) return p * p % d m = int(input()) d = 1000000007 ans = 0 for _ in range(m): n, s = map(int, input().split()) ans += s * power(n, d - 2) % d print(ans % d) 분할정복