Four people – A, B, C and D, started working on a project. It is known that, B is two-third as efficient as C, half as efficient as C and 50% more efficient than D. Each day, one of them takes a day-off. On Day 1, only A, B and C work together. On Day 2, only A, B and D work together. On Day 3, only B, C and D work together. On Day 4, only A, C and D work together. They repeat this four-day schedule until the project is completed. Had the project been completed by only C and D, working together every day, they would have taken 72 days to complete it. Among the total number of days they took to complete the project, how many days did C work?