#include <iostream>
using namespace std;

int main() 
{
	int n = 5;
	int op_limit = 1;
	int op_done = 0;
	bool add = true;
	int sum = 0;
	for(int i = 1; i <= n; ++i) {
	    if(op_done == op_limit) {
	        op_done = 0;
	        ++op_limit;
	        add = !add;
	    }
	    sum += (add? i : -i);
	    ++op_done;
	}
	std::cout << sum;
}