#include<iostream>
using namespace std;
int pre[10][10][10];
main()
{
	int a,b,c;
	long K;
	cin>>a>>b>>c>>K;
	a%=10;
	b%=10;
	c%=10;
	int now=3;
	K-=3;
	while(K>0)
	{
		pre[a][b][c]=now++;
		int d=(a+b+c)%10;
		a=b;b=c;c=d;
		K--;
		if(pre[a][b][c])K%=now-pre[a][b][c];
	}
	cout<<c<<endl;
}