#include <iostream>
using namespace std;

int main(){
	int op,a,b,k;
	cin >> op >> a >> b >> k;
	
	if(op == 1){
		a += b;
	}
	else if(op == 2){
		a -= b;
	}
	else if(op == 3){
		a *= b;
	}
	else{
		a -= k*b;
	}
	if(a < 0) a = 0;
	
	cout << a;
	
	return 0;
}