#include <iostream>

using namespace std;

int main()
{
    int N, A[32001], B[32001];
    cin >> N;
    cin >> A[1];
    int cnt = 0;
    if( A[1] )
    {
        B[1] = 1;
        for( int i = 2; i <= N; ++i )
        {
            cin >> A[i], B[i] = i % 2;
            if( A[i] != B[i] )
                cnt++;
        }
    }
    else
    {
        B[1] = 0;
        for( int i = 2; i <= N; ++i )
        {
            cin >> A[i], B[i] = (i - 1) % 2;
            if( A[i] != B[i] )
                cnt++;
        }
    }
    cout << cnt;
    return 0;
}