#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using db = double;
using ull = unsigned long long;
#define ff(x) fixed << setprecision(x)
#define vel vector<long long>
#define vei vector<int>
#define ves vector<string>
#define asn ans
constexpr int inf = 0x3f3f3f3f;
constexpr ll INF = 0x3f3f3f3f3f3f3f3fLL;
constexpr db EPS = 1.0e-9;
constexpr ll MOD = 998244353LL;
constexpr ll SZ = 1e6;
constexpr ll MAXN5 = 2e5 + 5;
constexpr ll MAXN6 = 2e6 + 5;
ll n, m;

void Solve(void){
    string s;
    cin>>s;
    int cnt=0;
    for(int i=0;i<s.size();i++){
        if(s[i]=='0'){
            cnt++;
        }
    }   
    int flag=0;
    ll i=1,j=s.size()-2;
    while(s[i]=='0'&&i<s.size()-1){
        i++;
    }
    while(s[j]=='0'&&j>0){
        j--;
    }  
    int ans=0;
    for(;i<=j;i++){
        if(s[i]=='0'){
            ans++;
        }
    }
 
    if(s[0]=='1'){
        ans++;
    }
    if(s[s.size()-1]=='1'){
        ans++;
    }
    cout<<min({(ll)ans,(ll)cnt,(ll)s.size()-cnt})<<'\n';
}
int main(void)
{
    ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    // 	freopen("mine.in", "r", stdin);
    // 	freopen("mine.out", "w", stdout);

    int cas = 1;
    // cin >> cas;
    while (cas--)
        Solve();
    return 0;
}