#include<bits/stdc++.h>
using namespace std;
const int MAXN=1e5+5; 
double a[MAXN];
int v[MAXN];
string str;
bool flag;
int cnt;
int main(){
	freopen("changgao_cost.in","r",stdin);
	freopen("changgao_cost.out","w",stdout);
	while(cin>>str);
	for(int i=0;i<str.length();i++){
		v[i+1]=str[i]-'0';
	}
	int n=str.length();
	for(int i=1;i<=n;i++){
		a[i]=i;
	}
	double x=a[n]+1;
	int l=1,r=n;
	while(l<=r){
		int mid=(l+r)/2;
		if(a[mid]>x){
			r=mid;
		}else l=mid+1;
		cnt+=v[mid];
	}
		cout<<cnt<<endl;
	return 0;
}