def sum_tail(n, s = 0):
	
	if n == 0:
		
	   return s
	   
	else:
		
	   return sum(n // 10, n % 10 + s)	

def sum( n ):
	
	if n == 0:
		
	   return 0
	   
	else:
		
	   return n % 10 + sum(n // 10)
	   

def main():
	
    n = int(input("n="))
    
    print(sum_tail(n)) 
	
main()