#include <bits/stdc++.h>
#define FASTIO
using namespace std;

using ll = long long;
using Vi = std::vector<int>;
using Vl = std::vector<ll>;
using Pii = std::pair<int, int>;
using Pll = std::pair<ll, ll>;

constexpr int I_INF = std::numeric_limits<int>::max();
constexpr ll L_INF = std::numeric_limits<ll>::max();

template <typename T1, typename T2>
inline bool chmin(T1& a, const T2& b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <typename T1, typename T2>
inline bool chmax(T1& a, const T2& b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <std::ostream& os = std::cout>
class Prints {
private:
    class __Prints {
    public:
        __Prints(const char* sep, const char* term) : sep(sep), term(term) {}
        template <class... Args>
#if __cplusplus >= 201703L
        auto operator()(const Args&... args) const -> decltype((os << ... << std::declval<Args>()), void()) {
#else
        void operator()(const Args&... args) const {
#endif
            print(args...);
        }
        template <typename T>
#if __cplusplus >= 201703L
        auto pvec(const T& vec, size_t sz) const -> decltype(os << std::declval<decltype(std::declval<T>()[0])>(), void()) {
#else
        void pvec(const T& vec, size_t sz) const {
#endif
            for (size_t i = 0; i < sz; i++)
                os << vec[i] << (i == sz - 1 ? term : sep);
        }
        template <typename T>
#if __cplusplus >= 201703L
        auto pmat(const T& mat, size_t h, size_t w) const -> decltype(os << std::declval<decltype(std::declval<T>()[0][0])>(), void()) {
#else
        void pmat(const T& mat, size_t h, size_t w) const {
#endif
            for (size_t i = 0; i < h; i++)
                for (size_t j = 0; j < w; j++)
                    os << mat[i][j] << (j == w - 1 ? term : sep);
        }

    private:
        const char *sep, *term;
        void print() const { os << term; }
        void print_rest() const { os << term; }
        template <class T, class... Tail>
        void print(const T& head, const Tail&... tail) const { os << head, print_rest(tail...); }
        template <class T, class... Tail>
        void print_rest(const T& head, const Tail&... tail) const { os << sep << head, print_rest(tail...); }
    };

public:
    Prints() {}
    __Prints operator()(const char* sep = " ", const char* term = "\n") const { return __Prints(sep, term); }
};

Prints<> prints;
Prints<std::cerr> prints_err;

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

ll nxt[1000][64];

void solve() {
    ll P, Q, R, K;
    cin >> P >> Q >> R >> K;
    P %= 10;
    Q %= 10;
    R %= 10;
    for (ll i = 0; i < 10; i++) {
        for (ll j = 0; j < 10; j++) {
            for (ll k = 0; k < 10; k++) {
                nxt[i * 100 + j * 10 + k][0] = j * 100 + k * 10 + ((i + j + k) % 10);
            }
        }
    }
    for (ll i = 0; i + 1 < 64; i++) {
        for (ll j = 0; j < 1000; j++) {
            nxt[j][i + 1] = nxt[nxt[j][i]][i];
        }
    }
    ll cur = 100 * P + 10 * Q + R;
    K -= 3;
    for (ll i = 0; i < 64; i++) {
        if (K >> i & 1) cur = nxt[cur][i];
    }
    prints()(cur % 10);
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

int main() {
#ifdef FASTIO
    std::cin.tie(nullptr), std::cout.tie(nullptr);
    std::ios::sync_with_stdio(false);
#endif
#ifdef FILEINPUT
    std::ifstream ifs("./in_out/input.txt");
    std::cin.rdbuf(ifs.rdbuf());
#endif
#ifdef FILEOUTPUT
    std::ofstream ofs("./in_out/output.txt");
    std::cout.rdbuf(ofs.rdbuf());
#endif
    std::cout << std::setprecision(18) << std::fixed;
    solve();
    std::cout << std::flush;
    return 0;
}