#include <bits/stdc++.h>
using namespace std;

int main() {
  int p, q, r;
  long long K;
  cin >> p >> q >> r >> K;
  K--;

  p %= 10, q %= 10, r %= 10;
  map<tuple<int, int, int>, int> seen;
  int i = 0;
  while (true) {
    if (!seen.count({p, q, r})) {
      seen[{p, q, r}] = i;
      int tmp = (p + q + r) % 10;
      p = q, q = r, r = tmp;
      i++;
    } else {
      break;
    }
  }

  int cycle_s = seen[{p, q, r}], cycle_e = i;
  int cycle_size = cycle_e - cycle_s;
  vector<int> cycle(cycle_e - cycle_s);
  for (auto [tup, order] : seen) {
    if (cycle_s <= order && order < cycle_e) {
      cycle[order - cycle_s] = get<0>(tup);
    }
  }

  K %= cycle_size;
  cout << cycle[K] << endl;

  return 0;
}