#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#define _GLIBCXX_DEBUG
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
ll I=1167167167167167167;
ll Q=10;
#define rep(i,a) for (ll i=0;i<a;i++)
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
template<class T> void print_tate(vector<T> &v) {rep(i,v.size()) cout<<v[i]<<"\n";}
void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";}


vector<vector<ll>> v_mul(vector<vector<ll>> a,vector<vector<ll>> b){
  int A=a.size(),B=a[0].size(),C=b.size(),D=b[0].size();
  vector<vector<ll>> r(A,vector<ll>(D));
  for(int i=0;i<A;i++){
    for(int k=0;k<B;k++){
      for(int j=0;j<D;j++){
        r[i][j]+=(a[i][k]*b[k][j])%Q;
		r[i][j]%=Q;
      }
    }
  }
  return r;
}
vector<vector<ll>> v_jyo(vector<vector<ll>> a,int64_t N){
  int m=a.size();
  ll H=1;
  vector<vector<ll>> r(m,vector<ll>(m,0));
  for(int i=0;i<m;i++){
    r[i][i]=1;
  }
  while(N>0){
    H*=2;
    if(N%H){
      N-=(H/2);
      r=v_mul(r,a);
    }
    a=v_mul(a,a);
  }
  return r;
}


//おちこんだりもしたけれど、私はげんきです。
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	ll p,q,r,K;
	cin>>p>>q>>r>>K;
	vector<vector<ll>> S={
		{0,0,1},
		{1,0,1},
		{0,1,1}
	};
	vector<vector<ll>> X(1,vector<ll>(3));
	X[0][0]=p,X[0][1]=q,X[0][2]=r;
	auto Y=v_mul(X,v_jyo(S,K-1));
	cout<<Y[0][0]%10<<endl;
}