#include <iostream>
#include <vector>
using namespace std;
std::vector<int> a;
int n,x,y;
int main()
{
    cin>>n;
    for(int i=1;i<=n;++i)
    {
        cin>>x;
        a.push_back(x);
    }
    y = 0;
    for(int i=1;i<=n;++i)
    {
        if((i%2==1&&a[i-1]==0)||(i%2==0&&a[i-1]==1))y++;
    }
    x = 0;
    for(int i=1;i<=n;++i)
    {
        if((i%2==0&&a[i-1]==0)||(i%2==1&&a[i-1]==1))x++;
    }
    if(x<y)cout<<x;
    else cout<<y;
    return 0;
}