1068. Сумма http://acm.timus.ru/problem.aspx?space=1&num=1068

1068.cpp

#include <iostream>

using namespace std;

int main()
{
#ifdef _DEBUG
    freopen("input.txt", "r",stdin);
    freopen("output.txt", "w",stdout);
#endif
   int num = 0;
   int a;
   cin >> a;

   if (a < 1) {
	   while (a <= 1) {
		   num += a;
		   a++;
	   }
   }
   else {
   	   while (a >= 1) {
		   num += a;
		   a--;
	   }
   }

   cout << num << endl;
   return 0;
}