How many NVMe PCIe can I install

Hello I have rack server power edge R640 with the below specifications

Chassis with Up to 10x2.5in HDD and 3 PCIe Slots

PCIe Riser Config 4, 2 x16 Low Profile

240GB SSD SATA M.2 512e 6Gbps Drive

My question, How many NVMe PCIe device I can add?

Please note that server is running in production and I cannot access it since it is abroad, so I have to take the correct decision