I was solving this problem with a combinatoric based approach. So I compute binomial coefficient using Fermat Little Th. and modular inverse. I have correct values for N up to 34, then my code starts giving wrong values. I belive the approach is correct but there is some issue I cant figure out related to modulo, modular inverse or powmod function. Can anybody help me understanding why my code fails? CODE

I might be wrong, but the 70'th line (

`ll half = nCk(n, n/2, mod)/2;`

) might mess your calculations up, maybe that`nCk`

returns an odd number but you divide it by 2. I suggest using`*inverse(2, mod)`

. I haven't verified the code logic so I cannot say if the approach is correct or not. Hope this helps.thank you very much, this is the actual issue. You made my day :D.