#include<iostream>
#include<vector>
using namespace std;
int main(){
    long p,q,r,k;cin >> p >> q >> r >> k;
    vector<int> calc(k);
    calc[0]=p%10;
    calc[1]=q%10;
    calc[2]=r%10;
    for(int i=3;i<k;i++){
        calc[i]=(calc[i-1]+calc[i-2]+calc[i-3])%10;
    }
    cout << calc[k-1] << endl;
    return 0;
}