#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (ll i=(ll)from; i<(ll)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (ll i=(ll)N-1; i>=0; i--)
#define popcount __builtin_popcount

const ll LLINF = pow(2,61)-1;
const ll INF = pow(2,30)-1;

ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }

int main() {
  vector<ll> A(3); rep(i,3) { cin >> A[i]; A[i] %= 10; }
  ll K; cin >> K; K--;
  ll np = 3;
  while (true) {
    ll X = (A[np-3]+A[np-2]+A[np-1]) % 10;
    A.push_back(X);
    if (A[np-2]==A[0]&&A[np-1]==A[1]&&A[np]==A[2]) break;
    np++;
  }
  // debug(all(A));
  np -= 2;
  ll result = A[K%np];
  cout << result << endl;
  return 0;
}