import std.algorithm, std.array, std.range;
import std.string, std.conv;
import std.math;
import std.stdio, std.typecons;

void main()
{
  auto rd = readln.split.map!(to!long);
  auto f = rd[0..2].array;
  auto n = rd[2];

  f ~= f[0] ^ f[1];

  writeln(f[n % 3]);
}