#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<functional>
#include<math.h>
#include<random>
#include <bitset>
#include <cassert>
#include <complex>
using namespace std;
//#define N (1000000000+7)
//#define N 998244353
#define INF 1e16
typedef long long ll;
typedef pair<ll,ll> P;
typedef pair<int,P> Q;


int main() {
    string s;
    cin>>s;
    int ans = 0;
    for(int i=0;i<s.size()-1;i++){
        if(s[i]!='0'){
            if(s[i+1]!='0')ans++;
        }
        else{
            if(s[i]=='0'){
                if(s[i+1]!='0')ans++;
            }
        }
    }
    cout<<ans<<endl;
}