#include <bits/stdc++.h>

using namespace std;

int a,b,k,x,hasil=1;

int absolut(int ubah){
	if(ubah<0){
		ubah= -1 * ubah;
	}
	return ubah;
}

int main(){
	cin>>a>>b>>k>>x;
	if(k<0){
		cout<<endl;
	}else{
		for(int z=1;z<=k;z++){
			x = absolut(a * absolut(x) + b);
		}
		cout<<x<<endl;
	}

	return 0;
}