//yukicoder@cpp17

#include <iostream>

#include <cmath>
#include <algorithm>

#include <iomanip>

#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <map>

#include <bitset>

#include <complex>

#include <cctype>
#include <utility>
#include <climits>

#include <numeric>

using namespace std;
using ll = long long;
using P = pair<ll,ll>;

const ll MOD = 998244353;
const ll MODx = 1000000007;
const int INF = (1<<30)-1;
const ll LINF = (1LL<<62LL)-1;
const double EPS = (1e-10);

P ar4[4] = {{0,1},{0,-1},{1,0},{-1,0}};
P ar8[8] = {{-1,-1},{-1,0},{-1,1},{0,-1},{0,1},{1,-1},{1,0},{1,1}};




template <typename T> vector<T> make_vector(size_t a, T b) { return vector<T>(a, b); }
template <typename... Ts> auto make_vector(size_t a, Ts... ts) { return vector<decltype(make_vector(ts...))>(a, make_vector(ts...)); }
 
 /*
確認ポイント
cout << fixed << setprecision(n) << 小数計算//n桁の小数表記になる

計算量は変わらないが楽できるシリーズ
min(max)_element(iter,iter)で一番小さい(大きい)値のポインタが帰ってくる
count(iter,iter,int)でintがiterからiterの間にいくつあったかを取得できる
*/

/*
function corner below
*/


/*
Function corner above
*/

struct x{
    long long a,b,c;
    bool operator==(const x A){
        return a == A.a && b == A.b && c == A.c;
    }
    bool operator!=(const x A){
        return !((*this) == A);
    }
};

bool operator<(const x B, const x A){
    if(B.a == A.a){
        if(B.b == A.b){
            return B.c < A.c;
        }
        return B.b < A.b;
    }
    return B.a < A.a;
}

__attribute__((constructor))
void initial() {
 cin.tie(0);
 ios::sync_with_stdio(false);
}

int main(){
    long long a,b,c,X;cin>>a>>b>>c>>X;
    X-=3;
    a %= 10;b %= 10; c %= 10;
    set<x> A;
    while(!A.count({a,b,c})){
        A.insert({a,b,c});
        int tmp = (a+b+c)%10;
        a = b;
        b = c;
        c = tmp;
        X--;
        if(!X){
            cout << tmp << endl;
            return 0;
        }
    }
    x goal = {a,b,c};
    long long ring = 0;
    int tmpx = (a+b+c)%10;
    a = b;
    b = c;
    c = tmpx;
    vector<x> Z;
    Z.push_back({a,b,c});
    while(goal != (x){a,b,c}){
        int tmp = (a+b+c)%10;
        a = b;
        b = c;
        c = tmp;
        Z.push_back({a,b,c});
    }
    cout << Z[X%Z.size()].b << endl;
}