Minecraft server Java Jvm arguments

I am trying to make a Minecraft Server but when i do it says the amount of allocated ram is 650 m and i want to allocate more i have 16 gigs of ram installed and i want to allocate 7 or 4 gigs of ram to it but when i try to make the command it says either invalid max heap size the specified size exceeds the max representable size Error: Could not create the java virtual machine Error: A fatal exception has occured. program will exit. i tried making the java option and editing the path but it wont work. i need a list of viable solutions

java --version

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