Timus Online Judge 1068. Sum Solution

1068. Sum
Language: c++

#include <iostream>

using namespace std;

int main()
{
    int N,sum;
    cin>>N;

    if(N>0)
          sum = N*(N+1)/2;

    else
        sum = (N*(N-1)/2-1)*-1;
    cout<<sum<<endl;


}