#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define MAXN 100010
inline ll read(){
	ll x=0,f=1;
	char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-')f=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9'){
		x=x*10+c-'0';
		c=getchar();
	}
	return x*f;
}
ll a[MAXN],len;
string s;
ll dfs1(ll l,ll r){
	if(l==r)return 0;
	ll mid=(l+r+1)/2;
	ll ans=max(dfs1(l,mid-1),dfs1(mid,r));
	return ans+a[mid];
}
ll dfs2(ll l,ll r){
	if(l==r)return 0;
	ll mid=(l+r)/2;
	ll ans=max(dfs2(l,mid),dfs2(mid+1,r));
	return ans+a[mid];
}
int main(){
	freopen("changgao_cost.in","r",stdin);
	freopen("changgao_cost.out","w",stdout);
	cin>>s;
	len=s.length();
	for(int i=0;i<len;i++){
		a[i+1]=s[i]-'0';
	}
	cout<<min(dfs1(0,len),dfs2(1,len+1));
	return 0;
}