include <stdio.h>

include

include

using namespace std;

int main() {

//freopen("number.in", "r", stdin);
//freopen("number.out", "w", stdout);
string a;
int s[9], d = 0;
getline(cin, a);
for (int i = 0; i <= 8; i++) {
	s[i] = a.size();
	if (a[i] == '1') {
		d++;
	}
}
printf("%d", d);
return 0;

}