#include<bits/stdc++.h>
#define ll long long
#define il inline
#define pn putchar('\n')
#define maxint 2147483647
#define min(x,y) (x<y?x:y)
#define max(x,y) (x>y?x:y)
#define maxn 1000005
using namespace std;
int n,las;
int f[maxn];
string s;
il bool check()
{
    for(int i=1;i<n;i++)
        if(s[i]=='1'&&s[i+1]=='0')
            return 0;
    return 1;
}
signed main()
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt","r",stdin);
    #endif
    cin>>s;
    n=s.size();
    s=' '+s;
    if(check())
        return puts("0"),0;
    for(int i=n;i;i--)
    {
        if(s[i]=='0')continue;
        if(n==i)f[i]=0;
        else
            f[i]=n-i+!(i&1);
        if(f[i]<f[las])
            f[i]=f[las]+1;
        las=i,n--;
    }
    printf("%d",f[las]);
    return 0;
}