The strange lotus leaf.
The new species of lotus leaf is growing in the swamp. It's size will increases everyday which it's size on today is bigger than yesterday for 2 times and grow continue in same pattern in the next day.
If the lotus leaf grows to the full area of swamp on day 10. It will grows to the half area of swamp on day n. "FIND n"
If there are 4 same lotus leaves in this swamp. How many days that they grow to the full area of swamp?