What is wrong with this sum of series code

Link to the problem will be helpful [if its any problem from spoj?]

What is !3 [!5, !7…] in this series?

long int == int [int32] on SPOJ [32bit system]
long long == long long int == [int64bit on 32 or 64 bit systems]

long int … sum, …
long long … sum = 0,

PS
I don’ t read your code very careful, but maybe it will be helpful:

sum = X
for (d = 5; d <= N; d += 4)
    sum += pow(X, d) / ! d; 
for (d = 3; d <= N; d += 4)
    sum -= pow(X, d) / ! d;