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:
| Launch date | Operator | Name | Sample origin | Samples returned | Recovery date | Mission result |
| --- | --- | --- | --- | --- | --- | --- |
| June 14, 1969 |  | Luna E-8-5 No.402 | The Moon | None | - | Failure\nLaunch failure |
| July 13, 1969 |  | Luna 15 | The Moon | None | - | Failure\nCrash-landed on the Moon |
| 23 September 1969 |  | Cosmos 300 | The Moon | None | - | Failure\nFailed to leave Earth orbit |
| 22 October 1969 |  | Cosmos 305 | The Moon | None | - | Failure\nFailed to leave Earth orbit |
| 6 February 1970 |  | Luna E-8-5 No.405 | The Moon | None | - | Failure\nLaunch failure |
| September 12, 1970 |  | Luna 16 | The Moon | 101 grams (3.6 oz)\nof lunar rock | September 24, 1970 | Success |
| September 2, 1971 |  | Luna 18 | The Moon | None | - | Failure\nCrash-landed on the Moon |
| February 14, 1972 |  | Luna 20 | The Moon | 55 grams (1.9 oz)\nof lunar rock | February 25, 1972 | Success |
| November 2, 1974 |  | Luna 23 | The Moon | None | - | Failure\nDrilling device damaged on Moon landing\nMission abandoned |
| October 16, 1975 |  | Luna E-8-5M No.412 | The Moon | None | - | Failure\nLaunch failure |
| August 9, 1976 |  | Luna 24 | The Moon | 170 grams (6.0 oz)\nof lunar rock | August 22, 1976 | Success |
| 1979 (planned)\n(canceled 1977) |  | Mars 79 ("Mars 5M") | Mars | - | - | Canceled in 1977\nPlanned to return 500 grams (18 oz) |
| February 7, 1999 |  | Stardust | 81P/Wild\n(Comet coma) | Over 1 million\ncomet particles | January 15, 2006 | Success |
| August 8, 2001 |  | Genesis | Solar wind | Solar wind particles | September 8, 2004 | Partial success\nReturn capsule damaged after failed parachute deployment\nSome usable samples recovered |
| May 9, 2003 |  | Hayabusa | 25143 Itokawa\n(Asteroid surface) | 1,500 grains\nof asteroid particles | June 13, 2010 | Partial success\nPlanned to return several hundred milligrams |
| November 8, 2011 |  | Fobos-Grunt | Phobos\n(Mars satellite soil) | None | - | Failure\nFailed to leave Earth orbit\nCrashed into the southern Pacific Ocean\nReturned none of the 200 grams (7.1 oz) planned |
| July 2014\n(planned, earliest) |  | Hayabusa 2 | Planned for\n(162173) 1999 JU3\n(Asteroid surface) | - | 2020 (planned) |  |
| 2016\n(planned) |  | OSIRIS-REx | Planned for\n101955 Bennu\n(Asteroid regolith) | - | 2023 (planned) | Planned to return between 60 g to 2 kg (2.1 oz to 4.4 lb) |
| 2017\n(planned) |  | Chang'e 5 | The Moon | - | 2017 (planned) | Planned to return at least 2 kilograms (4.4 lb) |
| 2020-2022\n(proposed) |  | MarcoPolo-R | Near-Earth object\n(Asteroid surface) | - | To be determined | To return samples from a yet to be determined near-Earth object |
| 2020/2021\n(planned) |  | Luna-Grunt | The Moon | - | 2021 (planned) | Planned to return up to 1 kilogram (2.2 lb) |
| Mid-2020s\n(proposed) |  | MEJI\nMSR | Mars | - | To be determined | To be determined |
| Mid-2020s\n(proposed) |  | Mars-Grunt | Mars | - | To be determined | Intended to return about 200 grams (7.1 oz) |
| By 2030 |  | Chinese Mars sample return mission | Mars | - | To be determined | To be determined |
| To be determined | (private) | OpenLuna | The Moon | - | To be determined | Intended to return about 200 kilograms (440 lb) |
Question:
what was the average amount of missions that were successful?
Answer:
4