What would happen to a person if they stayed on venus?

Without a Space Suit they would be stunk, suffocated and quickly roasted to death.

Details below...

Venus has a runaway Greenhouse gas type atmosphere.

The mass of the atmosphere of Venus is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen.

Plus there is Sulphar Dioxide in the Venus's atmosphere.

Surface temp is 425 °C.