#include <stdio.h>
#include <stdlib.h>
int sum (int n);
int sumToSingleDigit(int n);
int main()
{
  int n = 42535;
  printf("Final Sum of digits to single digit : %d\n",sumToSingleDigit(n));
  
  return 0;
}
int sum (int n)
{
  if(n<10)
    return n;
  
  int rem = n%10;
  int quo = n/10;
  return sum(quo) + rem;
}
int sumToSingleDigit(int n)
{
  if(n <10)
    return n;
  
  int sumOfDigits = sum(n);
  printf("Intermediate Sum : %d \n",sumOfDigits);
  return sumToSingleDigit(sumOfDigits);
}