#include "bits/stdc++.h"
using namespace std;
#define int long long
#define endl '\n'
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
  int a,b,k;
  cin>>a>>b>>k;
  int cnt=0;
  for(int i=100;i>0;i--){
    if(a%i==0&&b%i==0)cnt++;
    if(cnt==k){
      cout<<i<<endl;
      return 0;
    }
  }
}

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