Decryption of encrypted values with the repeated squaring algorithm

I have the following encryption algorithm and I want to know how to get the original value from the "Result" variable after exiting the loop.

InBytes = 2820389213912491205;
Result = 1;
Val = 0x3419;
while(Val != 0)
{
    if( (Val & 1) == 1)
    {
        Result = Result * InBytes; //Val is odd
    }
    InBytes = InBytes * InBytes;
    Val = Val / 2;
}

I would be glad if you could also link me to a source code example of the decryption algorithm.

P.S : The encryption is done on 64-bit values so bruteforce isn't really an option here.