#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}void pr(){ln;}
template<class A,class...B>void pr(const A &a,const B&...b){cout<<a<<(sizeof...(b)?" ":"");pr(b...);}
template<class A>void PR(A a,ll n){rep(i,n)cout<<(i?" ":"")<<a[i];ln;}
const ll MAX=1e9+7,MAXL=1LL<<61,dx[8]={-1,0,1,0,-1,-1,1,1},dy[8]={0,1,0,-1,-1,1,1,-1};
typedef pair<ll,ll> P;
typedef pair<P,ll> PP;

void Main() {
  ll x,y,z,k;
  cin >> x >> y >> z >> k;
  x%=10,y%=10,z%=10;
  k-=2;
  ll dp[10][10][10];
  memset(dp,-1,sizeof(dp));
  dp[x][y][z]=0;
  while(1) {
    k--;
    if(!k) {
      pr(z);
      return;
    }
    ll w=(x+y+z)%10;
    if(dp[y][z][w]!=-1) {
      k%=dp[x][y][z]-dp[y][z][w]+1;
      while(k) {
        x=y,y=z,z=w;
        w=(x+y+z)%10;
        k--;
      }
      pr(z);
      return;
    }
    dp[y][z][w]=dp[x][y][z]+1;
    x=y,y=z,z=w;
  }
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}