Wrote a python program that added up numbers from 1 to a given number using the Gauss equation. It worked for 100 and 10 but when I do 3 it says the sum is 4 instead of 6. The equation works out in my head, did I mess up the code?

```
def numberSum(num): 

    nim = int(num)
    num = (nim/2)*(nim+1)
    return num    

print numberSum(raw_input())  

```