#include <iostream>
using namespace std;

bool isPrime(int n)
{
  if( n < 2 ) return false;
  if( n == 2 || n == 3 ) return true;
  if( (n & 1) == 0 ) return false;
  for( int i = 3 ; i * i <= n ; i += 2 ) {
    if( n % i == 0 ) return false;
  }
  return true;
}

int main(void)
{
  int a, d, n;
  while( cin >> a >> d >> n ) {
    if( (a | d | n) == 0 ) break;
    do {
      if( isPrime(a) ) --n;
      a += d;
    } while( n );
    cout << (a - d) << endl;
  }
  return 0;
}