#include <iostream>
#include <math.h>

using namespace std;

long long n1, n2, k;

long long solve(long long n1, long long n2, long long k) {
	if (k == 1)
		return n1;
	if (k == 2)
		return n2;
	
	long long d = n1 > n2 ? n1 - n2 : n2 - n1;
	
	if ((n1 >= n2) && (n2 >= d)) {
		long long r = (k - 1) / 3;
		long long m = d > 0 ? n2 / (2*d) : r + 1;
		if (r > m)
			return solve(n2 - 2*d*m, d, k-1 - 3*m);
		else
			return (k % 3 == 1) ? n1 - r*2*d : ((k % 3 == 2) ? n2 - r*2*d : d);
	} else
		return solve(n2, d, k-1);
}

int main() {
	cin >> n1 >> n2 >> k;
	cout << solve(n1, n2, k) << endl;
	return 0;
}