'use strict'

function main(input) {
  input = input.split(' ').map(v => ~~v)

  const a = input[0]
  const b = input[1]
  const k = input[2]

  let cnt = []

  for (let i = 1; i <= 100; i++) {
    if (a % i == 0 && b % i == 0) {
      cnt.push(i)
      //   console.log(cnt, i)
    }
  }
  cnt.reverse()
  console.log(cnt.slice(k - 1).shift())
  //   console.log(gcd(input[0], input[1]))
  //   console.log(Math.min(cnt, input[2]))
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'))