windows 10 - How can I get maximum space to shrink from C drive

I have Bought new laptop which contains only C drive with 915.84 GB of space ,in which 874 GB is free ,when i want to partition the space ,the only available space to Shrink is 467994 MB [467.994 GB],why it is like ,can any one help me in this ,I need to keep C drive as 150GB and remaining space i want to shrink it to new drives

Thanks in Advance.