#include <iostream>

int main() {
    int n;
    std::cin >> n;
    int thousands = n / 1000;
    int hundreds = (n / 100) % 10;
    int tens = (n / 10) % 10;
    int units = n % 10;
    int digit_sum = thousands + hundreds + tens + units;
    std::cout << digit_sum << std::endl;
    return 0;
}    
/**************************************************************
	Problem: 1390
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/