#include<bits/stdc++.h>
using namespace std;

const int nmax=1e6+42;

int n;

char inp[nmax];

int solve()
{
    cin>>n;
    for(int i=1;i<=n;i++)cin>>inp[i];

    int outp=0;

    for(int i=1;i<n;i++)
        if(inp[i]=='1'&&inp[i+1]=='0')outp++;

    return outp;
}

int main()
{
    freopen("freddy.in","r",stdin);
    freopen("freddy.out","w",stdout);

    ios_base::sync_with_stdio(false);
    cin.tie();
    cout.tie();

    int t;
    t=1;

    while(t)
    {
        t--;
        cout<<solve()<<"\n";
    }

    return 0;
}