tpa rec5

#include <stdio.h>

int tohex(int x, int p) {
  if (x == 0) {
    return 0;
  }
  int dig = x % 10;
  return tohex(x / 10, 16 * p) + dig * p;
}

int main() {
  printf("%d\n", tohex(312, 1));
  return 0;
}