#include <iostream>
using namespace std;
int A, B, x, K;
int fungsi(){
if (K>0){
int tend;
K-=1;
tend= A*fungsi()+B;
if (tend<0){
return -1*(A*fungsi()+B);
}
else {
return A*fungsi()+B;
}
}
else {
return x;
}
}
int main(){
cin >> A >> B >> x >> K;
cout << fungsi();
}
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