#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;

void powmat(vector<vector<int>> &a,int n){
  auto b = a;
}

int main(){

  int p,q,r;
  ll k;
  cin >> p >> q >> r >> k;
  p %= 10;
  q %= 10;
  r %= 10;
  k --;
  vector<int> res = {p,q,r,(p+q+r)%10};
  int j= res.size()-3;
  while(res[0]!=res[j] || res[1]!=res[j+1] || res[2]!=res[j+2]) {
    res.push_back( (res[j] + res[j+1] + res[j+2])%10);
    j = res.size()-3;
  }

  cout << res[ k%(res.size()-3) ] << endl;


}