how to calculate the time and space complexity of this nested recursive function

问题

#include <stdio.h>
int fun(int n)
{
 if(n>100)
 return n-10;
 return fun(fun(n+11));
}
int main()
{
 int r;
 r=fun(95);
 printf("%d\n",r);
 return 0;
}

the answer says time complexity is O(n), can anyone explain how?

来源：https://stackoverflow.com/questions/62381491/how-to-calculate-the-time-and-space-complexity-of-this-nested-recursive-function