Const is not constant

#include<stdio.h>

void main() {
  const int is_this_really_a_constant = 1;
  int *not_so = &is_this_really_a_constant;
  *not_so = 0;
  if (is_this_really_a_constant) {
      puts("const really means constant");
  } else {
      puts("const means read-only");
  }
}