In the problem STFM of FEB long challenge, my approach got AC for two sub tasks. It failed when value of x increased. After looking at the editorial, I tried it again with my approach with the mod trick(that factorial becomes zero). Now it is giving WA for all subtasks. I am unable to find my mistake. Can any one help please?

can you explain your approach?

Try including this:

```
#define nmod(num ,modValue) (modValue-((-num)%modValue))
```

Pass the values where there is a chance of getting negative values and you have to calculate the mod

Here is my approach. Since we have to calculate the values for different f§, if p1<p2, p2 will have same calculations as p1 plus some additional calculations. To reduce it, I sorted the values p1<=p2<=…<=pn.

So I calculated factorial part from 1 to pn(largest p) and whenever the value of iterator became equal to pi(less than pn), I added the value to result. Now, when the value of iterator became greater than mod, I stopped the calculations and stored the present factorial value. Now for all pi>=mod, f(pi) will be equal to f(mod-1). So I added this value to result for rest of the pi (i>=mod). This concludes the factorial part.

For the second part, i.e. the sum from 1 to pi (for all pi), I simply calculated it using Arithmetic progression formula and added to the result.