function main(arg) {
   a = arg.split(" ");
   x = a[0];
   y = a[1];
   z = a[2];
   incr = 0;

       for(var i=x*y; i> 0; i--){

           if(x%i === 0 && y%i === 0){

             incr++;
             if(incr == z){console.log(i);}

            }
       }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));