function Main(input){
	input = input.split(" ").map(a=>~~a);
  var A = input.shift();
  var B = input.shift();
  var K = input.shift();
  
  var m = Math.min(A,B);
  var cnt = 0;
	for(var i = m; 1 <= i;i--){
  	if(A%i == 0 && B%i == 0){
    	cnt++;
      if(cnt==K)return i;
    }
  }  
}

// If you are interested in the algorithms I used, 
// there is no need to read down from this line.

((b,c,d)=>"undefined"!=typeof require?console.log(Main(require("fs").readFileSync("/dev/stdin","utf8"))):[b=b.split("\n").slice(1,-1).join("\n"),c=function(){try{return Main(b)}catch(f){return f.stack||f.message}}(),d=typeof c,"string"==d||(c=JSON.stringify(c)),$("<form>").append([[10,b],0,[1,d],0,[10,c]].map(f=>$(f?"<textarea>":"<br>",f&&{rows:f[0],cols:40,text:f[1]}))).appendTo("body")])(`
100 50 4
`);