import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.typecons;
import std.numeric, std.math;
import core.bitop;

string FMT_F = "%.10f";

T RD(T = long)() { static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
bool minimize(T)(ref T x, T y) { if (x > y) { x = y; return true; } else { return false; } }
bool maximize(T)(ref T x, T y) { if (x < y) { x = y; return true; } else { return false; } }

long mod = 10^^9 + 7;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

void main()
{
	auto A = RD;
	auto B = RD;
	auto K = RD;

	long ans;
	foreach_reverse (i; 1..min(A, B)+1)
	{
		if (A % i == 0 && B % i == 0) 
		{
			--K;
			//stderr.writeln(i);
		}
		if (K == 0)
		{
			ans = i;
			break;
		}
	}

	writeln(ans);
	stdout.flush();
}