Hello,
Many programming exercises require working with BigInteger. C#'s BigInteger is not in the default group of DLLs the compiler uses to generate an exe. This limits significantly the usability of C# under SPOJ. Java's got its BigInteger by default, so there's no problem. Could you please include this dll (System.Numerics.dll) as part of the default compilation for C# submissions? It shouldn't be more than
gmcs -optimize+ -reference:System.Numerics.dll