while
  a,d,n = gets.split(" ")
  a = a.to_i
  d = d.to_i
  n = n.to_i

  i = 0
  prime = 0
  primeNum = 0
  judge = false

  if a == 0 && d == 0 && n == 0
    break
  end

  unless a == 0 && d == 0 && n == 0
    while !judge do
      sum = a + (d*i)

      primejudge = true
      if sum == 1
        primejudge = false
      end

      for num in 2..(sum-1) do
        if sum % num == 0
          primejudge = false
          break
        end
      end

      if primejudge
        primeNum = primeNum + 1
        if primeNum == n
          prime = sum
          judge = true
          break
        end
      end
      i=i+1
    end
    puts prime
  end
end