#include <iostream>
using namespace std;
int fungsi(int a, int b,int k, int c){
int r = c;
if(k > 0){
r = a*fungsi(a,b,k-1,c) + b;
if (r < 0){
r *= -1;
}
}
return r;
}
int main(){
int A, B, K, x;
cin >> A >> B >> K >> x;
cout << fungsi(A,B,K,x) <<endl;
return 0;
}
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