#include <iostream>
#include<cstdio>
#include<cstring>
using namespace std;

int v[33000],n,a,b;


int main()
{
//freopen("date.in","r",stdin);
//freopen("date.out","w",stdout);
cin>>n;
for(int i=1; i<=n; i++)
{
 scanf("%d",&v[i]);
}

for(int i=1; i<=n; i++)
{
    if(i%2!=v[i])a++;
    if((i+1)%2 != v[i])b++;
}
if(a>b)cout<<b<<"\n";
else cout<<a<<"\n";
    return 0;
}