#include<bits/stdc++.h>
using namespace std;
int main(){
    string s;
    cin >> s;
    int count = 0;
    // 用s.size()动态获取长度，而非硬编码8
    for(int i = 0; i < s.size(); i++){
        if(s[i] == '1'){
            count++;
        }
    }
    cout << count << endl; // 确保输出后换行
    return 0;
}

/**************************************************************
	Problem: 1934
	User: zhengzihao
	Language: C++
	Result: Wrong Answer
****************************************************************/