#include<bits/stdc++.h>
using namespace std;
int main()
{
    freopen("freddy.in","r",stdin);
    freopen("freddy.out","w",stdout);
    int n;
    cin>>n;
    string s;
    cin>>s;
    int br=0,otg=0;
    for(int i=0;i<n;i++)
    {
        if(s[i]=='1')br++;
        if(s[i]=='0')
        {
            if(br)otg++;
            br=0;
        }
    }
    cout<<otg<<endl;
}