a and b using the formula lcm(a, b) = (a * b) / gcd(a, b), where gcd is the greatest common divisor.low = 0 and high = n * min(a, b).low is less than high:
a. Calculate mid = (low + high) / 2.
b. Calculate the number of magical numbers less than or equal to mid using the formula f(mid).
c. If f(mid) is less than n, set low = mid + 1.
d. If f(mid) is greater than or equal to n, set high = mid.low % (10^9 + 7) as the nth magical number.