Please write in Python 3

You will be given a single positive integer and perform repeated addition of its digits until the result has a single digit. The process works as follows: Number Digit sum 93874 9+3+8+7+4-31 31 3+1-4 So the repeated digit sum of 93874 is 4. It turns out the the repeated digit sum of any number divisible by 9 is always 9. For example, 925 717,897,987,691,852,588, 770, 249 and it's repeated digit sum can be calculated as: Nxolxar 717897987691852588770249 7+17+8+9+7+9+8+7+6+9+1+8 Digit sum +5+2+5+8+8+8+7+7+0+2 +4+9-144 1+4+4-9 144 Input A single positive integer. Output The repeated digit sum (which has a single digit.) Example sessions 93874 4 717897987691852588770249