'use strict'

const gcd = (m, n) => {
  return n ? gcd(n, m % n) : m
}
function main(input) {
  input = input.split(' ').map(v => ~~v)

  const a = input[0]
  const b = input[1]
  const k = input[2]
  let cnt = 0
//   console.log(a, b, k)

  for (let i = 1; i <= 100; i++) {
    if (a % i == 0 && b % i == 0) {
      cnt++
    //   console.log(cnt, i)

      if (cnt == k) {
        console.log(i)
        return
      }
    }
  }

  //   console.log(gcd(input[0], input[1]))
  //   console.log(Math.min(cnt, input[2]))
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'))