Possible Int/Long Conflict? (ADDNATRL)

Hello,

I used the Gauss summation method for ADDNATRL (Add Natural Numbers). I think the math itself is fine. To my understanding, long was discontinued in Python 3, so I have used type int in my solution. Test cases work as expected, including the maximum N = 10^9, but when I submitted my solution, it was marked as incorrect. I am not sure what I am doing wrong. Any advice would be greatly appreciated.

https://www.codechef.com/viewsolution/54370421

N = int(input())
print(int(N*(N+1)/2))