#include<bits/stdc++.h>
using namespace std;
using ll =long long ;
vector<ll>a1,a0;
ll b1[100],b0[100];
ll dp[100][5];
int main()
{
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	string s;
	cin>>s;
	ll n=s.size();
	ll f=0;
	for(ll i=0;i<n;i++)
	{
		if(s[i]=='1')
		{
			f=1;
			ll j;
			for(j=i;j<n;j++)
			{
				if(s[j]!=s[i])
				{
					break;
				}
			}
			a1.push_back(j-i);
			i=j-1;
		}
		else if(s[i]=='0'&&f==1)
		{
			ll j;
			for(j=i;j<n;j++)
			{
				if(s[j]!=s[i])
				{
					break;
				}
				
			}
			a1.push_back(j-i);
			i=j-1;
		}
	}
	ll l1=a1.size(),ff=0,ans=0,i,sum=0;
	a1.push_back(0);
	a1.push_back(0);
	if(l1%2==0&&l1!=0)
	{
		a1[l1-1]=0;
		l1--;
	}
	for(i=0;i<l1;i+=2) 
	{
		if(a1[i]>=a1[i+1])
		{
			ans+=a1[i+1];
			i+=2;
			break;
		}
		ans+=a1[i];
	}
	ll j;
	
	for(j=i;j<l1;j+=2)
	{
		dp[j+1][0]=dp[j-1][0]+a1[j+1];
		dp[j+1][1]=min(dp[j-1][1],dp[j-1][0])+a1[j+2];
	}
	
	cout<<min(dp[j-1][0],dp[j-1][1])+ans<<'\n';
}