#include<bits/stdc++.h> 
using namespace std;
typedef long long ll;
#define all(x) (x).begin(),(x).end()
template<typename T1,typename T2> bool chmin(T1 &a,T2 b){if(a<=b)return 0; a=b; return 1;}
template<typename T1,typename T2> bool chmax(T1 &a,T2 b){if(a>=b)return 0; a=b; return 1;}
int dx[4]={0,1,0,-1}, dy[4]={1,0,-1,0};
long double eps = 1e-9;
long double pi = acos(-1);


signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout << fixed << setprecision(20);

	ll a,b,c,k;
	cin>>a>>b>>c>>k;
	k--;
	a%=10;
	b%=10;
	c%=10;
	int now = 1;
	ll tail = 0, roop = 0;
	vector<int> cnt(1000,-1);
	now = 3;
	cnt[a] = 0;
	cnt[a*10+b] = 1;
	cnt[a*100 + b*10 + c] = 2;
	while(true){
		int nx = (a + b + c)%10;
		a = b, b = c, c = nx;
		int pos = a*100 + b*10 + c;
		// cerr << now << " " << nx << endl;
		if(k == now){
			cout << nx << endl;
			return 0;
		}
		if(cnt[pos]!=-1){
			tail = cnt[pos];
			roop = now - cnt[pos];
			break;
		}
		cnt[pos] = now;
		now++;
	}
	k -= tail;
	k %= roop;
	cerr << tail << " " << roop << endl;
	for(int i=0;i<1000;i++){
		if(cnt[i]== k + tail){
			cout << i % 10 << endl;
			return 0;
		}
	}
}