n = int(input())
q = n // 1000 % 10
b = n // 100 % 10
s = n // 10 % 10
g = n // 1 % 10
su = q + b + s + g
print(su)
/**************************************************************
	Problem: 1390
	User: admin
	Language: Python
	Result: Accepted
	Time:181 ms
	Memory:34244 kb
****************************************************************/