#include<iostream>
#include<fstream>
using namespace std;
bool prime[1000000];
int main(){
  	ifstream cin("./A1");
  	ofstream cout("./oa.txt");
	prime[0]=prime[1]=1;
	
	for(int i=2;i<1000000;++i)
		if(prime[i]==0){
			for(int j=i+i;j<1000000;j+=i)
				prime[j]=1;
		}
	int a,b,c;
	while(cin >> a >> b >> c,a|b|c){
		int wc = 0;
		for(;;a+=b){
			if(prime[a]==0 && ++wc == c){
				cout << a << endl;
				break;
			}
		}
	}
}