#include <iostream>
using namespace std;
int main()
{
    int v[32001],i,n,cont=0;
    cin>>n;
    for (i=1; i<=n; i++)
    cin>>v[i];

    for (i=1; i<=n-1; i++)
    if (v[i]==v[i+1])
    {
        v[i+1]=(v[i+1]+1) % 2;
        cont++;
    }
    cout<<cont<<'\n';
    return 0;
}