a, b, t = gets.split.map &:to_i
ans = 10**18
0.upto(a) do |i|
	re = t - i * b

	if re <= 0
		cost = i * b
		ans = cost if ans > cost
		break
	end
	j = (re + a - 1) / a
	cost = i * b + j * a
	ans = cost if ans > cost
end
puts ans