Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Rank | Name | Headquarters | Industry | Market value ( USD million) |
| --- | --- | --- | --- | --- |
| 1.0 | Exxon Mobil | United States | Oil and gas | 371631.0 |
| 2.0 | General Electric | United States | Conglomerate | 362527.0 |
| 3.0 | Microsoft | United States | Software industry | 281171.0 |
| 4.0 | Citigroup | United States | Banking | 238935.0 |
| 5.0 | BP | United Kingdom | Oil and gas | 233260.0 |
| 6.0 | Bank of America | United States | Banking | 211706.0 |
| 7.0 | Royal Dutch Shell | The Netherlands | Oil and gas | 211280.0 |
| 8.0 | Wal-Mart | United States | Retail | 196860.0 |
| 9.0 | Toyota Motor Corporation | Japan | Automotive | 196731.0 |
| 10.0 | Gazprom | Russia | Oil and gas | 196339.0 |
Question:
What is the lowest rank of Citigroup?
Answer:
4.0