The following code giving answer 21. I am not understanding how the operators are working

Question

#include<stdio.h>

int main()
{
  int i = 10;
  int d = ++i + i--;
  printf ("d = %d\n",d);
  return 0;
    }

This code printing d = 21. The order of evaluation is taken right to left and left to right, but still the answer is not evaluating to 21.