C++ :

#include <iostream>
using namespace std;
unsigned int func(long long x,long long y,long long z){
	for(long long  i=1;i<=z*2;i++){
		if(y<=0)
			return 0;
		if(i%2==1)
			y -= x; 			
		if(i%4 == 0)
			y *= 2;
		if(i%6 == 0)
			x *= 2; 	
	}
	return y;		
}
int main(){
	for(long long x,y,z;cin>>x>>y>>z;)
		cout<<func(x,y,z)<<endl; 
	return 0;
}