模板题

def ex_gcd(a, b):
    if b == 0:
        return 1, 0, a 
    else:
        x, y, gcd = ex_gcd(b, a % b)
        return y, x - a // b * y, gcd

def cal(r1, m1, r2, m2):
    _, _, d = ex_gcd(m1, m2)
    if (r2 - r1) % d != 0:
        return -1, -1
    k1, k2, _ = ex_gcd(m1 // d, m2 // d)
    k1 = (r2 - r1) // d * k1
    mm = m1 * m2 // d 
    rr = (r1 + k1 * m1) % mm 
    return rr, mm 

n = int(input())
r, m = [], []
for _ in range(n):
    mm, rr = map(int, input().split())
    r.append(rr)
    m.append(mm)

rr, mm = r[0], m[0]
for i in range(1, n):
    rr, mm = cal(rr, mm, r[i], m[i])
    if rr == -1:
        break 
print(rr)